// Copyright (c) 2010 The WebM project authors. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS.  All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.

#include "mkvparser.hpp"
#include <cassert>
#include <cstring>
#include <new>
#include <climits>

mkvparser::IMkvReader::~IMkvReader()
{
}

void mkvparser::GetVersion(int& major, int& minor, int& build, int& revision)
{
    major = 1;
    minor = 0;
    build = 0;
    revision = 20;
}

long long mkvparser::ReadUInt(IMkvReader* pReader, long long pos, long& len)
{
    assert(pReader);
    assert(pos >= 0);

    int status;

//#ifdef _DEBUG
//    long long total, available;
//    status = pReader->Length(&total, &available);
//    assert(status >= 0);
//    assert((total < 0) || (available <= total));
//    assert(pos < available);
//    assert((available - pos) >= 1);  //assume here max u-int len is 8
//#endif

    len = 1;

    unsigned char b;

    status = pReader->Read(pos, 1, &b);

    if (status < 0)  //error or underflow
        return status;

    if (status > 0)  //interpreted as "underflow"
        return E_BUFFER_NOT_FULL;

    if (b == 0)  //we can't handle u-int values larger than 8 bytes
        return E_FILE_FORMAT_INVALID;

    unsigned char m = 0x80;

    while (!(b & m))
    {
        m >>= 1;
        ++len;
    }

//#ifdef _DEBUG
//    assert((available - pos) >= len);
//#endif

    long long result = b & (~m);
    ++pos;

    for (int i = 1; i < len; ++i)
    {
        status = pReader->Read(pos, 1, &b);

        if (status < 0)
        {
            len = 1;
            return status;
        }

        if (status > 0)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result <<= 8;
        result |= b;

        ++pos;
    }

    return result;
}

long long mkvparser::GetUIntLength(
    IMkvReader* pReader,
    long long pos,
    long& len)
{
    assert(pReader);
    assert(pos >= 0);

    long long total, available;

    int status = pReader->Length(&total, &available);
    assert(status >= 0);
    assert((total < 0) || (available <= total));

    len = 1;

    if (pos >= available)
        return pos;  //too few bytes available

    unsigned char b;

    status = pReader->Read(pos, 1, &b);

    if (status < 0)
        return status;

    assert(status == 0);

    if (b == 0)  //we can't handle u-int values larger than 8 bytes
        return E_FILE_FORMAT_INVALID;

    unsigned char m = 0x80;

    while (!(b & m))
    {
        m >>= 1;
        ++len;
    }

    return 0;  //success
}

long long mkvparser::SyncReadUInt(
    IMkvReader* pReader,
    long long pos,
    long long stop,
    long& len)
{
    assert(pReader);

    if (pos >= stop)
        return E_FILE_FORMAT_INVALID;

    unsigned char b;

    long hr = pReader->Read(pos, 1, &b);

    if (hr < 0)
        return hr;

    if (hr != 0L)
        return E_BUFFER_NOT_FULL;

    if (b == 0)  //we can't handle u-int values larger than 8 bytes
        return E_FILE_FORMAT_INVALID;

    unsigned char m = 0x80;
    len = 1;

    while (!(b & m))
    {
        m >>= 1;
        ++len;
    }

    if ((pos + len) > stop)
        return E_FILE_FORMAT_INVALID;

    long long result = b & (~m);
    ++pos;

    for (int i = 1; i < len; ++i)
    {
        hr = pReader->Read(pos, 1, &b);

        if (hr < 0)
            return hr;

        if (hr != 0L)
            return E_BUFFER_NOT_FULL;

        result <<= 8;
        result |= b;

        ++pos;
    }

    return result;
}


long long mkvparser::UnserializeUInt(
    IMkvReader* pReader,
    long long pos,
    long long size)
{
    assert(pReader);
    assert(pos >= 0);
    assert(size > 0);
    assert(size <= 8);

    long long result = 0;

    for (long long i = 0; i < size; ++i)
    {
        unsigned char b;

        const long status = pReader->Read(pos, 1, &b);

        if (status < 0)
            return status;

        result <<= 8;
        result |= b;

        ++pos;
    }

    return result;
}


float mkvparser::Unserialize4Float(
    IMkvReader* pReader,
    long long pos)
{
    assert(pReader);
    assert(pos >= 0);

#ifdef _DEBUG
    {
        long long total, available;

        const long status = pReader->Length(&total, &available);
        assert(status >= 0);
        assert((total < 0) || (available <= total));
        assert((pos + 4) <= available);
    }
#endif

#if 0
    float result;

    unsigned char* const p = (unsigned char*)&result;
    unsigned char* q = p + 4;

    for (;;)
    {
        hr = pReader->Read(pos, 1, --q);
        assert(hr == 0L);

        if (q == p)
            break;

        ++pos;
    }
#else
    union
    {
        float result;
        unsigned long buf;
    };

    buf = 0;

    for (int i = 0;;)
    {
        unsigned char b;

        const int status = pReader->Read(pos++, 1, &b);

        if (status < 0)  //error
            return static_cast<float>(status);

        buf |= b;

        if (++i >= 4)
            break;

        buf <<= 8;
    }
#endif

    return result;
}


double mkvparser::Unserialize8Double(
    IMkvReader* pReader,
    long long pos)
{
    assert(pReader);
    assert(pos >= 0);

#if 0
    double result;

    unsigned char* const p = (unsigned char*)&result;
    unsigned char* q = p + 8;

    for (;;)
    {
        const long hr = pReader->Read(pos, 1, --q);
        assert(hr == 0L);

        if (q == p)
            break;

        ++pos;
    }
#else
    union
    {
        double result;
        long long buf;
    };

    buf = 0;

    for (int i = 0;;)
    {
        unsigned char b;

        const int status = pReader->Read(pos++, 1, &b);

        if (status < 0)  //error
            return static_cast<double>(status);

        buf |= b;

        if (++i >= 8)
            break;

        buf <<= 8;
    }
#endif

    return result;
}

signed char mkvparser::Unserialize1SInt(
    IMkvReader* pReader,
    long long pos)
{
    assert(pReader);
    assert(pos >= 0);

#ifdef _DEBUG
    {
        long long total, available;

        const long status = pReader->Length(&total, &available);
        assert(status == 0);
        assert((total < 0) || (available <= total));
        assert(pos < available);
    }
#endif

    signed char result;
    unsigned char& b = reinterpret_cast<unsigned char&>(result);

    const int status = pReader->Read(pos, 1, &b);
    assert(status == 0);  //TODO: must be handled somehow

    return result;
}

short mkvparser::Unserialize2SInt(
    IMkvReader* pReader,
    long long pos)
{
    assert(pReader);
    assert(pos >= 0);

#ifdef _DEBUG
    {
        long long total, available;

        const long status = pReader->Length(&total, &available);
        assert(status >= 0);
        assert((total < 0) || (available <= total));
        assert((pos + 2) <= available);
    }
#endif

#if 0
    short result;

    unsigned char* const p = (unsigned char*)&result;
    unsigned char* q = p + 2;

    for (;;)
    {
        hr = pReader->Read(pos, 1, --q);
        assert(hr == 0L);

        if (q == p)
            break;

        ++pos;
    }
#else
    short result = 0;

    for (int i = 0;;)
    {
        unsigned char b;

        const int status = pReader->Read(pos++, 1, &b);
        assert(status == 0);  //TODO: must be handled somehow

        result |= b;

        if (++i >= 2)
            break;

        result <<= 8;
    }
#endif

    return result;
}


bool mkvparser::Match(
    IMkvReader* pReader,
    long long& pos,
    unsigned long id_,
    long long& val)
{
    assert(pReader);
    assert(pos >= 0);

    long long total, available;

    const long status = pReader->Length(&total, &available);
    assert(status >= 0);
    assert((total < 0) || (available <= total));

    long len;

    const long long id = ReadUInt(pReader, pos, len);
    assert(id >= 0);
    assert(len > 0);
    assert(len <= 8);
    assert((pos + len) <= available);

    if ((unsigned long)id != id_)
        return false;

    pos += len;  //consume id

    const long long size = ReadUInt(pReader, pos, len);
    assert(size >= 0);
    assert(size <= 8);
    assert(len > 0);
    assert(len <= 8);
    assert((pos + len) <= available);

    pos += len;  //consume length of size of payload

    val = UnserializeUInt(pReader, pos, size);
    assert(val >= 0);

    pos += size;  //consume size of payload

    return true;
}

bool mkvparser::Match(
    IMkvReader* pReader,
    long long& pos,
    unsigned long id_,
    char*& val)
{
    assert(pReader);
    assert(pos >= 0);

    long long total, available;

    long status = pReader->Length(&total, &available);
    assert(status >= 0);
    assert((total < 0) || (available <= total));

    long len;

    const long long id = ReadUInt(pReader, pos, len);
    assert(id >= 0);
    assert(len > 0);
    assert(len <= 8);
    assert((pos + len) <= available);

    if ((unsigned long)id != id_)
        return false;

    pos += len;  //consume id

    const long long size_ = ReadUInt(pReader, pos, len);
    assert(size_ >= 0);
    assert(len > 0);
    assert(len <= 8);
    assert((pos + len) <= available);

    pos += len;  //consume length of size of payload
    assert((pos + size_) <= available);

    const size_t size = static_cast<size_t>(size_);
    val = new char[size+1];

    for (size_t i = 0; i < size; ++i)
    {
        char c;

        status = pReader->Read(pos + i, 1, (unsigned char*)&c);
        assert(status == 0);  //TODO

        val[i] = c;

        if (c == '\0')
            break;
    }

    val[size] = '\0';
    pos += size_;  //consume size of payload

    return true;
}

bool mkvparser::Match(
    IMkvReader* pReader,
    long long& pos,
    unsigned long id_,
    unsigned char*& buf,
    size_t& buflen)
{
    assert(pReader);
    assert(pos >= 0);

    long long total, available;

    long status = pReader->Length(&total, &available);
    assert(status >= 0);
    assert((total < 0) || (available <= total));

    long len;
    const long long id = ReadUInt(pReader, pos, len);
    assert(id >= 0);
    assert(len > 0);
    assert(len <= 8);
    assert((pos + len) <= available);

    if ((unsigned long)id != id_)
        return false;

    pos += len;  //consume id

    const long long size_ = ReadUInt(pReader, pos, len);
    assert(size_ >= 0);
    assert(len > 0);
    assert(len <= 8);
    assert((pos + len) <= available);

    pos += len;  //consume length of size of payload
    assert((pos + size_) <= available);

    const long buflen_ = static_cast<long>(size_);

    buf = new (std::nothrow) unsigned char[buflen_];
    assert(buf);  //TODO

    status = pReader->Read(pos, buflen_, buf);
    assert(status == 0);  //TODO

    buflen = buflen_;

    pos += size_;  //consume size of payload
    return true;
}


bool mkvparser::Match(
    IMkvReader* pReader,
    long long& pos,
    unsigned long id_,
    double& val)
{
    assert(pReader);
    assert(pos >= 0);

    long long total, available;

    const long status = pReader->Length(&total, &available);
    assert(status >= 0);
    assert((total < 0) || (available <= total));

    long idlen;

    const long long id = ReadUInt(pReader, pos, idlen);
    assert(id >= 0);  //TODO

    if ((unsigned long)id != id_)
        return false;

    long sizelen;
    const long long size = ReadUInt(pReader, pos + idlen, sizelen);

    switch (size)
    {
        case 4:
        case 8:
            break;
        default:
            return false;
    }

    pos += idlen + sizelen;  //consume id and size fields
    assert((pos + size) <= available);

    if (size == 4)
        val = Unserialize4Float(pReader, pos);
    else
    {
        assert(size == 8);
        val = Unserialize8Double(pReader, pos);
    }

    pos += size;  //consume size of payload

    return true;
}


bool mkvparser::Match(
    IMkvReader* pReader,
    long long& pos,
    unsigned long id_,
    short& val)
{
    assert(pReader);
    assert(pos >= 0);

    long long total, available;

    const long status = pReader->Length(&total, &available);
    assert(status >= 0);
    assert((total < 0) || (available <= total));

    long len;
    const long long id = ReadUInt(pReader, pos, len);
    assert(id >= 0);
    assert((pos + len) <= available);

    if ((unsigned long)id != id_)
        return false;

    pos += len;  //consume id

    const long long size = ReadUInt(pReader, pos, len);
    assert(size <= 2);
    assert((pos + len) <= available);

    pos += len;  //consume length of size of payload
    assert((pos + size) <= available);

    //TODO:
    // Generalize this to work for any size signed int
    if (size == 1)
        val = Unserialize1SInt(pReader, pos);
    else
        val = Unserialize2SInt(pReader, pos);

    pos += size;  //consume size of payload

    return true;
}


namespace mkvparser
{

EBMLHeader::EBMLHeader() :
    m_docType(NULL)
{
    Init();
}

EBMLHeader::~EBMLHeader()
{
    delete[] m_docType;
}

void EBMLHeader::Init()
{
    m_version = 1;
    m_readVersion = 1;
    m_maxIdLength = 4;
    m_maxSizeLength = 8;

    if (m_docType)
    {
        delete[] m_docType;
        m_docType = NULL;
    }

    m_docTypeVersion = 1;
    m_docTypeReadVersion = 1;
}

long long EBMLHeader::Parse(
    IMkvReader* pReader,
    long long& pos)
{
    assert(pReader);

    long long total, available;

    long status = pReader->Length(&total, &available);

    if (status < 0)  //error
        return status;

    pos = 0;
    long long end = (available >= 1024) ? 1024 : available;

    for (;;)
    {
        unsigned char b = 0;

        while (pos < end)
        {
            status = pReader->Read(pos, 1, &b);

            if (status < 0)  //error
                return status;

            if (b == 0x1A)
                break;

            ++pos;
        }

        if (b != 0x1A)
        {
            if (pos >= 1024)
                return E_FILE_FORMAT_INVALID;  //don't bother looking anymore

            if ((total >= 0) && ((total - available) < 5))
                return E_FILE_FORMAT_INVALID;

            return available + 5;  //5 = 4-byte ID + 1st byte of size
        }

        if ((total >= 0) && ((total - pos) < 5))
            return E_FILE_FORMAT_INVALID;

        if ((available - pos) < 5)
            return pos + 5;  //try again later

        long len;

        const long long result = ReadUInt(pReader, pos, len);

        if (result < 0)  //error
            return result;

        if (result == 0x0A45DFA3)  //EBML Header ID
        {
            pos += len;  //consume ID
            break;
        }

        ++pos;  //throw away just the 0x1A byte, and try again
    }

    //pos designates start of size field

    //get length of size field

    long len;
    long long result = GetUIntLength(pReader, pos, len);

    if (result < 0)  //error
        return result;

    if (result > 0)  //need more data
        return result;

    assert(len > 0);
    assert(len <= 8);

    if ((total >= 0) && ((total -  pos) < len))
        return E_FILE_FORMAT_INVALID;

    if ((available - pos) < len)
        return pos + len;  //try again later

    //get the EBML header size

    result = ReadUInt(pReader, pos, len);

    if (result < 0)  //error
        return result;

    pos += len;  //consume size field

    //pos now designates start of payload

    if ((total >= 0) && ((total - pos) < result))
        return E_FILE_FORMAT_INVALID;

    if ((available - pos) < result)
        return pos + result;

    end = pos + result;

    Init();

    while (pos < end)
    {
        if (Match(pReader, pos, 0x0286, m_version))
            ;
        else if (Match(pReader, pos, 0x02F7, m_readVersion))
            ;
        else if (Match(pReader, pos, 0x02F2, m_maxIdLength))
            ;
        else if (Match(pReader, pos, 0x02F3, m_maxSizeLength))
            ;
        else if (Match(pReader, pos, 0x0282, m_docType))
            ;
        else if (Match(pReader, pos, 0x0287, m_docTypeVersion))
            ;
        else if (Match(pReader, pos, 0x0285, m_docTypeReadVersion))
            ;
        else
        {
            result = ReadUInt(pReader, pos, len);
            assert(result > 0);
            assert(len > 0);
            assert(len <= 8);

            pos += len;
            assert(pos < end);

            result = ReadUInt(pReader, pos, len);
            assert(result >= 0);
            assert(len > 0);
            assert(len <= 8);

            pos += len + result;
            assert(pos <= end);
        }
    }

    assert(pos == end);
    return 0;
}


Segment::Segment(
    IMkvReader* pReader,
    long long start,
    long long size) :
    m_pReader(pReader),
    m_start(start),
    m_size(size),
    m_pos(start),
    m_pUnknownSize(0),
    m_pSeekHead(NULL),
    m_pInfo(NULL),
    m_pTracks(NULL),
    m_pCues(NULL),
    m_clusters(NULL),
    m_clusterCount(0),
    m_clusterPreloadCount(0),
    m_clusterSize(0)
{
}


Segment::~Segment()
{
    const long count = m_clusterCount + m_clusterPreloadCount;

    Cluster** i = m_clusters;
    Cluster** j = m_clusters + count;

    while (i != j)
    {
        Cluster* const p = *i++;
        assert(p);

        delete p;
    }

    delete[] m_clusters;

    delete m_pTracks;
    delete m_pInfo;
    delete m_pCues;
    delete m_pSeekHead;
}


long long Segment::CreateInstance(
    IMkvReader* pReader,
    long long pos,
    Segment*& pSegment)
{
    assert(pReader);
    assert(pos >= 0);

    pSegment = NULL;

    long long total, available;

    const long status = pReader->Length(&total, &available);

    if (status < 0) //error
        return status;

    if (available < 0)
        return -1;

    if ((total >= 0) && (available > total))
        return -1;

    const long long end = (total >= 0) ? total : available;
    //TODO: this might need to be liberalized

    //I would assume that in practice this loop would execute
    //exactly once, but we allow for other elements (e.g. Void)
    //to immediately follow the EBML header.  This is fine for
    //the source filter case (since the entire file is available),
    //but in the splitter case over a network we should probably
    //just give up early.  We could for example decide only to
    //execute this loop a maximum of, say, 10 times.
    //TODO:
    //There is an implied "give up early" by only parsing up
    //to the available limit.  We do do that, but only if the
    //total file size is unknown.  We could decide to always
    //use what's available as our limit (irrespective of whether
    //we happen to know the total file length).  This would have
    //as its sense "parse this much of the file before giving up",
    //which a slightly different sense from "try to parse up to
    //10 EMBL elements before giving up".

    while (pos < end)
    {
        //Read ID

        long len;
        long long result = GetUIntLength(pReader, pos, len);

        if (result)  //error, or too few available bytes
            return result;

        if ((pos + len) > end)
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > available)
            return pos + len;

        const long long id = ReadUInt(pReader, pos, len);

        if (id < 0)  //error
            return id;

        pos += len;  //consume ID

        //Read Size

        result = GetUIntLength(pReader, pos, len);

        if (result)  //error, or too few available bytes
            return result;

        if ((pos + len) > end)
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > available)
            return pos + len;

        long long size = ReadUInt(pReader, pos, len);

        if (size < 0)  //error
            return size;

        pos += len;  //consume length of size of element

        //Pos now points to start of payload

        //Handle "unknown size" for live streaming of webm files.
        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (id == 0x08538067)  //Segment ID
        {
            if (size == unknown_size)
                size = -1;

            else if (total < 0)
                size = -1;

#if 0  //this turned out to be too conservative:
            else if ((pos + size) > end)
                return E_FILE_FORMAT_INVALID;
#else  //so do this instead
            else if ((pos + size) > total)
                size = -1;
#endif

            pSegment = new (std::nothrow) Segment(pReader, pos, size);

            if (pSegment == 0)
                return -1;  //generic error

            return 0;    //success
        }

        if (size == unknown_size)
            return E_FILE_FORMAT_INVALID;

        if ((pos + size) > end)
            return E_FILE_FORMAT_INVALID;

        pos += size;  //consume payload
    }

    return E_FILE_FORMAT_INVALID;  //there is no segment
    //TODO: this might need to be liberalized.  See comments above.
}


long long Segment::ParseHeaders()
{
    //Outermost (level 0) segment object has been constructed,
    //and pos designates start of payload.  We need to find the
    //inner (level 1) elements.
    long long total, available;

    const int status = m_pReader->Length(&total, &available);
    assert(status == 0);
    assert((total < 0) || (available <= total));

    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;
    assert((segment_stop < 0) || (total < 0) || (segment_stop <= total));
    assert((segment_stop < 0) || (m_pos <= segment_stop));

    for (;;)
    {
        if ((total >= 0) && (m_pos >= total))
            break;

        if ((segment_stop >= 0) && (m_pos >= segment_stop))
            break;

        long long pos = m_pos;
        const long long element_start = pos;

        if ((pos + 1) > available)
            return (pos + 1);

        long len;
        long long result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return result;

        if (result > 0)  //underflow (weird)
            return (pos + 1);

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > available)
            return pos + len;

        const long long idpos = pos;
        const long long id = ReadUInt(m_pReader, idpos, len);

        if (id < 0)  //error
            return id;

        if (id == 0x0F43B675)  //Cluster ID
            break;

        pos += len;  //consume ID

        if ((pos + 1) > available)
            return (pos + 1);

        //Read Size
        result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return result;

        if (result > 0)  //underflow (weird)
            return (pos + 1);

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > available)
            return pos + len;

        const long long size = ReadUInt(m_pReader, pos, len);

        if (size < 0)  //error
            return size;

        pos += len;  //consume length of size of element

        const long long element_size = size + pos - element_start;

        //Pos now points to start of payload

        if ((segment_stop >= 0) && ((pos + size) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        //We read EBML elements either in total or nothing at all.

        if ((pos + size) > available)
            return pos + size;

        if (id == 0x0549A966)  //Segment Info ID
        {
            assert(m_pInfo == NULL);

            m_pInfo = new SegmentInfo(this,
                                      pos,
                                      size,
                                      element_start,
                                      element_size);
            assert(m_pInfo);  //TODO
        }
        else if (id == 0x0654AE6B)  //Tracks ID
        {
            assert(m_pTracks == NULL);

            m_pTracks = new Tracks(this,
                                   pos,
                                   size,
                                   element_start,
                                   element_size);
            assert(m_pTracks);  //TODO
        }
        else if (id == 0x0C53BB6B)  //Cues ID
        {
            if (m_pCues == NULL)
            {
                m_pCues = new Cues(this,
                                   pos,
                                   size,
                                   element_start,
                                   element_size);
                assert(m_pCues);  //TODO
            }
        }
        else if (id == 0x014D9B74)  //SeekHead ID
        {
#if 0
            if (available >= total)
                ParseSeekHead(pos, size);
#else
            if (m_pSeekHead == NULL)
            {
                m_pSeekHead = new SeekHead(this,
                                           pos,
                                           size,
                                           element_start,
                                           element_size);

                assert(m_pSeekHead);  //TODO
            }
#endif
        }

        m_pos = pos + size;  //consume payload
    }

    assert((segment_stop < 0) || (m_pos <= segment_stop));

    if (m_pInfo == NULL)  //TODO: liberalize this behavior
        return E_FILE_FORMAT_INVALID;

    if (m_pTracks == NULL)
        return E_FILE_FORMAT_INVALID;

    return 0;  //success
}


#if 0
long Segment::FindNextCluster(long long& pos, size& len) const
{
    //Outermost (level 0) segment object has been constructed,
    //and pos designates start of payload.  We need to find the
    //inner (level 1) elements.
    long long total, available;

    const int status = m_pReader->Length(&total, &available);
    assert(status == 0);
    assert(total >= 0);
    assert(available <= total);

    const long long stop = m_start + m_size;
    assert(stop <= total);
    assert(m_pos <= stop);

    pos = m_pos;

    while (pos < stop)
    {
        long long result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)
            return static_cast<long>(result);

        if (result > 0)
            return E_BUFFER_NOT_FULL;

        if ((pos + len) > stop)
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > available)
            return E_BUFFER_NOT_FULL;

        const long long idpos = pos;
        const long long id = ReadUInt(m_pReader, idpos, len);

        if (id < 0)  //error
            return static_cast<long>(id);

        pos += len;  //consume ID

        //Read Size
        result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)
            return E_BUFFER_NOT_FULL;

        if ((pos + len) > stop)
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > available)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(m_pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        pos += len;  //consume length of size of element

        //Pos now points to start of payload

        if ((pos + size) > stop)
            return E_FILE_FORMAT_INVALID;

        if ((pos + size) > available)
            return E_BUFFER_NOT_FULL;

        if (id == 0x0F43B675)  //Cluster ID
        {
            len = static_cast<long>(size);
            return 0;  //success
        }

        pos += size;  //consume payload
    }

    return E_FILE_FORMAT_INVALID;
}
#endif


#if 0
long Segment::ParseCluster(long long& off, long long& new_pos) const
{
    off = -1;
    new_pos = -1;

    const long long stop = m_start + m_size;
    assert(m_pos <= stop);

    long long pos = m_pos;

    while (pos < stop)
    {
        long len;
        const long long idpos = pos;

        const long long id = SyncReadUInt(m_pReader, pos, stop, len);

        if (id < 0)  //error
            return static_cast<long>(id);

        if (id == 0)
            return E_FILE_FORMAT_INVALID;

        pos += len;  //consume id
        assert(pos < stop);

        const long long size = SyncReadUInt(m_pReader, pos, stop, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        pos += len;  //consume size
        assert(pos <= stop);

        if (size == 0)  //weird
            continue;

        //pos now points to start of payload

        pos += size;  //consume payload
        assert(pos <= stop);

        if (id == 0x0F43B675)  //Cluster ID
        {
            const long long off_ = idpos - m_start;

            if (Cluster::HasBlockEntries(this, off_))
            {
                off = off_;   // >= 0 means we found a cluster
                break;
            }
        }
    }

    assert(pos <= stop);

    //Indicate to caller how much of file has been consumed. This is
    //used later in AddCluster to adjust the current parse position
    //(the value cached in the segment object itself) to the
    //file position value just past the cluster we parsed.

    if (off < 0)  //we did not found any more clusters
    {
        new_pos = stop;  //pos >= 0 here means EOF (cluster is NULL)
        return 0;        //TODO: confirm this return value
    }

    //We found a cluster.  Now read something, to ensure that it is
    //fully loaded in the network cache.

    if (pos >= stop)  //we parsed the entire segment
    {
        //We did find a cluster, but it was very last element in the segment.
        //Our preference is that the loop above runs 1 1/2 times:
        //the first pass finds the cluster, and the second pass
        //finds the element the follows the cluster.  In this case, however,
        //we reached the end of the file without finding another element,
        //so we didn't actually read anything yet associated with "end of the
        //cluster".  And we must perform an actual read, in order
        //to guarantee that all of the data that belongs to this
        //cluster has been loaded into the network cache.  So instead
        //of reading the next element that follows the cluster, we
        //read the last byte of the cluster (which is also the last
        //byte in the file).

        //Read the last byte of the file. (Reading 0 bytes at pos
        //might work too -- it would depend on how the reader is
        //implemented.  Here we take the more conservative approach,
        //since this makes fewer assumptions about the network
        //reader abstraction.)

        unsigned char b;

        const int result = m_pReader->Read(pos - 1, 1, &b);
        assert(result == 0);

        new_pos = stop;
    }
    else
    {
        long len;
        const long long idpos = pos;

        const long long id = SyncReadUInt(m_pReader, pos, stop, len);

        if (id < 0)  //error
            return static_cast<long>(id);

        if (id == 0)
            return E_BUFFER_NOT_FULL;

        pos += len;  //consume id
        assert(pos < stop);

        const long long size = SyncReadUInt(m_pReader, pos, stop, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        new_pos = idpos;
    }

    return 0;
}


bool Segment::AddCluster(long long off, long long pos)
{
    assert(pos >= m_start);

    const long long stop = m_start + m_size;
    assert(pos <= stop);

    if (off >= 0)
    {
        Cluster* const pCluster = Cluster::Parse(this,
                                                 m_clusterCount,
                                                 off,
                                                 0,
                                                 0);
        assert(pCluster);

        AppendCluster(pCluster);
        assert(m_clusters);
        assert(m_clusterSize > pCluster->m_index);
        assert(m_clusters[pCluster->m_index] == pCluster);
    }

    m_pos = pos;  //m_pos >= stop is now we know we have all clusters
    return (pos >= stop);
}
#endif


long Segment::LoadCluster(
    long long& pos,
    long& len)
{
    for (;;)
    {
        const long result = DoLoadCluster(pos, len);

        if (result <= 1)
            return result;
    }
}


long Segment::DoLoadCluster(
    long long& pos,
    long& len)
{
    if (m_pos < 0)
        return DoLoadClusterUnknownSize(pos, len);

    long long total, avail;

    long status = m_pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;

    long long cluster_off = -1;   //offset relative to start of segment
    long long cluster_size = -1;  //size of cluster payload

    for (;;)
    {
        if ((total >= 0) && (m_pos >= total))
            return 1;  //no more clusters

        if ((segment_stop >= 0) && (m_pos >= segment_stop))
            return 1;  //no more clusters

        pos = m_pos;

        //Read ID

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long idpos = pos;
        const long long id = ReadUInt(m_pReader, idpos, len);

        if (id < 0)  //error (or underflow)
            return static_cast<long>(id);

        pos += len;  //consume ID

        //Read Size

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(m_pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        pos += len;  //consume length of size of element

        //pos now points to start of payload

        if (size == 0)  //weird
        {
            m_pos = pos;
            continue;
        }

        const long long unknown_size = (1LL << (7 * len)) - 1;

#if 0  //we must handle this to support live webm
        if (size == unknown_size)
            return E_FILE_FORMAT_INVALID;  //TODO: allow this
#endif

        if ((segment_stop >= 0) &&
            (size != unknown_size) &&
            ((pos + size) > segment_stop))
        {
            return E_FILE_FORMAT_INVALID;
        }

#if 0  //commented-out, to support incremental cluster parsing
        len = static_cast<long>(size);

        if ((pos + size) > avail)
            return E_BUFFER_NOT_FULL;
#endif

        if (id == 0x0C53BB6B)  //Cues ID
        {
            if (size == unknown_size)
                return E_FILE_FORMAT_INVALID;  //TODO: liberalize

            if (m_pCues == NULL)
            {
                const long long element_size = (pos - idpos) + size;

                m_pCues = new Cues(this,
                                   pos,
                                   size,
                                   idpos,
                                   element_size);
                assert(m_pCues);  //TODO
            }

            m_pos = pos + size;  //consume payload
            continue;
        }

        if (id != 0x0F43B675)  //Cluster ID
        {
            if (size == unknown_size)
                return E_FILE_FORMAT_INVALID;  //TODO: liberalize

            m_pos = pos + size;  //consume payload
            continue;
        }

        //We have a cluster.

        cluster_off = idpos - m_start;  //relative pos

        if (size != unknown_size)
            cluster_size = size;

        break;
    }

    assert(cluster_off >= 0);  //have cluster

    long long pos_;
    long len_;

    status = Cluster::HasBlockEntries(this, cluster_off, pos_, len_);

    if (status < 0) //error, or underflow
    {
        pos = pos_;
        len = len_;

        return status;
    }

    //status == 0 means "no block entries found"
    //status > 0 means "found at least one block entry"

    //TODO:
    //The issue here is that the segment increments its own
    //pos ptr past the most recent cluster parsed, and then
    //starts from there to parse the next cluster.  If we
    //don't know the size of the current cluster, then we
    //must either parse its payload (as we do below), looking
    //for the cluster (or cues) ID to terminate the parse.
    //This isn't really what we want: rather, we really need
    //a way to create the curr cluster object immediately.
    //The pity is that cluster::parse can determine its own
    //boundary, and we largely duplicate that same logic here.
    //
    //Maybe we need to get rid of our look-ahead preloading
    //in source::parse???
    //
    //As we're parsing the blocks in the curr cluster
    //(in cluster::parse), we should have some way to signal
    //to the segment that we have determined the boundary,
    //so it can adjust its own segment::m_pos member.
    //
    //The problem is that we're asserting in asyncreadinit,
    //because we adjust the pos down to the curr seek pos,
    //and the resulting adjusted len is > 2GB.  I'm suspicious
    //that this is even correct, but even if it is, we can't
    //be loading that much data in the cache anyway.

    const long idx = m_clusterCount;

    if (m_clusterPreloadCount > 0)
    {
        assert(idx < m_clusterSize);

        Cluster* const pCluster = m_clusters[idx];
        assert(pCluster);
        assert(pCluster->m_index < 0);

        const long long off = pCluster->GetPosition();
        assert(off >= 0);

        if (off == cluster_off)  //preloaded already
        {
            if (status == 0)  //no entries found
                return E_FILE_FORMAT_INVALID;

            if (cluster_size >= 0)
                pos += cluster_size;
            else
            {
                const long long element_size = pCluster->GetElementSize();

                if (element_size <= 0)
                    return E_FILE_FORMAT_INVALID;  //TODO: handle this case

                pos = pCluster->m_element_start + element_size;
            }

            pCluster->m_index = idx;  //move from preloaded to loaded
            ++m_clusterCount;
            --m_clusterPreloadCount;

            m_pos = pos;  //consume payload
            assert((segment_stop < 0) || (m_pos <= segment_stop));

            return 0;  //success
        }
    }

    if (status == 0)  //no entries found
    {
        if (cluster_size < 0)
            return E_FILE_FORMAT_INVALID;  //TODO: handle this

        pos += cluster_size;

        if ((total >= 0) && (pos >= total))
        {
            m_pos = total;
            return 1;  //no more clusters
        }

        if ((segment_stop >= 0) && (pos >= segment_stop))
        {
            m_pos = segment_stop;
            return 1;  //no more clusters
        }

        m_pos = pos;
        return 2;  //try again
    }

    //status > 0 means we have an entry

    Cluster* const pCluster = Cluster::Create(this,
                                              idx,
                                              cluster_off);
                                              //element_size);
    assert(pCluster);

    AppendCluster(pCluster);
    assert(m_clusters);
    assert(idx < m_clusterSize);
    assert(m_clusters[idx] == pCluster);

    if (cluster_size >= 0)
    {
        pos += cluster_size;

        m_pos = pos;
        assert((segment_stop < 0) || (m_pos <= segment_stop));

        return 0;
    }

    m_pUnknownSize = pCluster;
    m_pos = -pos;

    return 0;  //partial success, since we have a new cluster

    //status == 0 means "no block entries found"

    //pos designates start of payload
    //m_pos has NOT been adjusted yet (in case we need to come back here)

#if 0

    if (cluster_size < 0)  //unknown size
    {
        const long long payload_pos = pos;  //absolute pos of cluster payload

        for (;;)  //determine cluster size
        {
            if ((total >= 0) && (pos >= total))
                break;

            if ((segment_stop >= 0) && (pos >= segment_stop))
                break;  //no more clusters

            //Read ID

            if ((pos + 1) > avail)
            {
                len = 1;
                return E_BUFFER_NOT_FULL;
            }

            long long result = GetUIntLength(m_pReader, pos, len);

            if (result < 0)  //error
                return static_cast<long>(result);

            if (result > 0)  //weird
                return E_BUFFER_NOT_FULL;

            if ((segment_stop >= 0) && ((pos + len) > segment_stop))
                return E_FILE_FORMAT_INVALID;

            if ((pos + len) > avail)
                return E_BUFFER_NOT_FULL;

            const long long idpos = pos;
            const long long id = ReadUInt(m_pReader, idpos, len);

            if (id < 0)  //error (or underflow)
                return static_cast<long>(id);

            //This is the distinguished set of ID's we use to determine
            //that we have exhausted the sub-element's inside the cluster
            //whose ID we parsed earlier.

            if (id == 0x0F43B675)  //Cluster ID
                break;

            if (id == 0x0C53BB6B)  //Cues ID
                break;

            switch (id)
            {
                case 0x20:  //BlockGroup
                case 0x23:  //Simple Block
                case 0x67:  //TimeCode
                case 0x2B:  //PrevSize
                    break;

                default:
                    assert(false);
                    break;
            }

            pos += len;  //consume ID (of sub-element)

            //Read Size

            if ((pos + 1) > avail)
            {
                len = 1;
                return E_BUFFER_NOT_FULL;
            }

            result = GetUIntLength(m_pReader, pos, len);

            if (result < 0)  //error
                return static_cast<long>(result);

            if (result > 0)  //weird
                return E_BUFFER_NOT_FULL;

            if ((segment_stop >= 0) && ((pos + len) > segment_stop))
                return E_FILE_FORMAT_INVALID;

            if ((pos + len) > avail)
                return E_BUFFER_NOT_FULL;

            const long long size = ReadUInt(m_pReader, pos, len);

            if (size < 0)  //error
                return static_cast<long>(size);

            pos += len;  //consume size field of element

            //pos now points to start of sub-element's payload

            if (size == 0)  //weird
                continue;

            const long long unknown_size = (1LL << (7 * len)) - 1;

            if (size == unknown_size)
                return E_FILE_FORMAT_INVALID;  //not allowed for sub-elements

            if ((segment_stop >= 0) && ((pos + size) > segment_stop))  //weird
                return E_FILE_FORMAT_INVALID;

            pos += size;  //consume payload of sub-element
            assert((segment_stop < 0) || (pos <= segment_stop));
        }  //determine cluster size

        cluster_size = pos - payload_pos;
        assert(cluster_size >= 0);

        pos = payload_pos;  //reset and re-parse original cluster
    }

    if (m_clusterPreloadCount > 0)
    {
        assert(idx < m_clusterSize);

        Cluster* const pCluster = m_clusters[idx];
        assert(pCluster);
        assert(pCluster->m_index < 0);

        const long long off = pCluster->GetPosition();
        assert(off >= 0);

        if (off == cluster_off)  //preloaded already
            return E_FILE_FORMAT_INVALID;  //subtle
    }

    m_pos = pos + cluster_size;  //consume payload
    assert((segment_stop < 0) || (m_pos <= segment_stop));

    return 2;     //try to find another cluster

#endif

}


long Segment::DoLoadClusterUnknownSize(
    long long& pos,
    long& len)
{
    assert(m_pos < 0);
    assert(m_pUnknownSize);

#if 0
    assert(m_pUnknownSize->GetElementSize() < 0);  //TODO: verify this

    const long long element_start = m_pUnknownSize->m_element_start;

    pos = -m_pos;
    assert(pos > element_start);

    //We have already consumed the (cluster) ID and size fields.
    //We just need to consume the blocks and other sub-elements
    //of this cluster, until we discover the boundary.

    long long total, avail;

    long status = m_pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;

    long long element_size = -1;

    for (;;)  //determine cluster size
    {
        if ((total >= 0) && (pos >= total))
        {
            element_size = total - element_start;
            assert(element_size > 0);

            break;
        }

        if ((segment_stop >= 0) && (pos >= segment_stop))
        {
            element_size = segment_stop - element_start;
            assert(element_size > 0);

            break;
        }

        //Read ID

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long idpos = pos;
        const long long id = ReadUInt(m_pReader, idpos, len);

        if (id < 0)  //error (or underflow)
            return static_cast<long>(id);

        //This is the distinguished set of ID's we use to determine
        //that we have exhausted the sub-element's inside the cluster
        //whose ID we parsed earlier.

        if ((id == 0x0F43B675) || (id == 0x0C53BB6B)) //Cluster ID or Cues ID
        {
            element_size = pos - element_start;
            assert(element_size > 0);

            break;
        }

#ifdef _DEBUG
        switch (id)
        {
            case 0x20:  //BlockGroup
            case 0x23:  //Simple Block
            case 0x67:  //TimeCode
            case 0x2B:  //PrevSize
                break;

            default:
                assert(false);
                break;
        }
#endif

        pos += len;  //consume ID (of sub-element)

        //Read Size

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(m_pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        pos += len;  //consume size field of element

        //pos now points to start of sub-element's payload

        if (size == 0)  //weird
            continue;

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size == unknown_size)
            return E_FILE_FORMAT_INVALID;  //not allowed for sub-elements

        if ((segment_stop >= 0) && ((pos + size) > segment_stop))  //weird
            return E_FILE_FORMAT_INVALID;

        pos += size;  //consume payload of sub-element
        assert((segment_stop < 0) || (pos <= segment_stop));
    }  //determine cluster size

    assert(element_size >= 0);

    m_pos = element_start + element_size;
    m_pUnknownSize = 0;

    return 2;  //continue parsing
#else
    const long status = m_pUnknownSize->Parse(pos, len);

    if (status < 0)  //error or underflow
        return status;

    if (status == 0)  //parsed a block
        return 2;     //continue parsing

    assert(status > 0);   //nothing left to parse of this cluster

    const long long start = m_pUnknownSize->m_element_start;

    const long long size = m_pUnknownSize->GetElementSize();
    assert(size >= 0);

    pos = start + size;
    m_pos = pos;

    m_pUnknownSize = 0;

    return 2;  //continue parsing
#endif
}


void Segment::AppendCluster(Cluster* pCluster)
{
    assert(pCluster);
    assert(pCluster->m_index >= 0);

    const long count = m_clusterCount + m_clusterPreloadCount;

    long& size = m_clusterSize;
    assert(size >= count);

    const long idx = pCluster->m_index;
    assert(idx == m_clusterCount);

    if (count >= size)
    {
        long n;

        if (size > 0)
            n = 2 * size;
        else if (m_pInfo == 0)
            n = 2048;
        else
        {
            const long long ns = m_pInfo->GetDuration();

            if (ns <= 0)
                n = 2048;
            else
            {
                const long long sec = (ns + 999999999LL) / 1000000000LL;
                n = static_cast<long>(sec);
            }
        }

        Cluster** const qq = new Cluster*[n];
        Cluster** q = qq;

        Cluster** p = m_clusters;
        Cluster** const pp = p + count;

        while (p != pp)
            *q++ = *p++;

        delete[] m_clusters;

        m_clusters = qq;
        size = n;
    }

    if (m_clusterPreloadCount > 0)
    {
        assert(m_clusters);

        Cluster** const p = m_clusters + m_clusterCount;
        assert(*p);
        assert((*p)->m_index < 0);

        Cluster** q = p + m_clusterPreloadCount;
        assert(q < (m_clusters + size));

        for (;;)
        {
            Cluster** const qq = q - 1;
            assert((*qq)->m_index < 0);

            *q = *qq;
            q = qq;

            if (q == p)
                break;
        }
    }

    m_clusters[idx] = pCluster;
    ++m_clusterCount;
}


void Segment::PreloadCluster(Cluster* pCluster, ptrdiff_t idx)
{
    assert(pCluster);
    assert(pCluster->m_index < 0);
    assert(idx >= m_clusterCount);

    const long count = m_clusterCount + m_clusterPreloadCount;

    long& size = m_clusterSize;
    assert(size >= count);

    if (count >= size)
    {
        long n;

        if (size > 0)
            n = 2 * size;
        else if (m_pInfo == 0)
            n = 2048;
        else
        {
            const long long ns = m_pInfo->GetDuration();

            if (ns <= 0)
                n = 2048;
            else
            {
                const long long sec = (ns + 999999999LL) / 1000000000LL;
                n = static_cast<long>(sec);
            }
        }

        Cluster** const qq = new Cluster*[n];
        Cluster** q = qq;

        Cluster** p = m_clusters;
        Cluster** const pp = p + count;

        while (p != pp)
            *q++ = *p++;

        delete[] m_clusters;

        m_clusters = qq;
        size = n;
    }

    assert(m_clusters);

    Cluster** const p = m_clusters + idx;

    Cluster** q = m_clusters + count;
    assert(q >= p);
    assert(q < (m_clusters + size));

    while (q > p)
    {
        Cluster** const qq = q - 1;
        assert((*qq)->m_index < 0);

        *q = *qq;
        q = qq;
    }

    m_clusters[idx] = pCluster;
    ++m_clusterPreloadCount;
}


long Segment::Load()
{
    assert(m_clusters == NULL);
    assert(m_clusterSize == 0);
    assert(m_clusterCount == 0);
    //assert(m_size >= 0);

    //Outermost (level 0) segment object has been constructed,
    //and pos designates start of payload.  We need to find the
    //inner (level 1) elements.

    long long total, avail;

    long status = m_pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;

    for (;;)
    {
        long long pos = m_pos;

        if ((total >= 0) && (pos >= total))
            break;

        if ((segment_stop >= 0) && (pos >= segment_stop))
            break;

        const long long element_start = pos;

        long len;

        long long result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        const long long idpos = pos;
        const long long id = ReadUInt(m_pReader, idpos, len);

        if (id < 0)  //error
            return static_cast<long>(id);

        pos += len;  //consume ID

        //Read Size
        result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        const long long size = ReadUInt(m_pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size == unknown_size)
            return E_FILE_FORMAT_INVALID;

        pos += len;  //consume length of size of element

        //Pos now points to start of payload

        const long long element_size = (pos - element_start) + size;

        if ((segment_stop >= 0) && ((pos + size) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if (id == 0x0F43B675)  //Cluster ID
        {
            const long idx = m_clusterCount;
            const long long off = idpos - m_start;

            long long pos_;
            long len_;

            status = Cluster::HasBlockEntries(this, off, pos_, len_);

            if (status < 0)  //weird: error or underflow
                return status;

            if (status > 0)  //have block entries
            {
                Cluster* const pCluster = Cluster::Create(this,
                                                         idx,
                                                         off);
                                                         //element_size);
                assert(pCluster);

                AppendCluster(pCluster);
                assert(m_clusters);
                assert(m_clusterSize > idx);
                assert(m_clusters[idx] == pCluster);
            }
        }
        else if (id == 0x0C53BB6B)  //Cues ID
        {
            assert(m_pCues == NULL);

            m_pCues = new Cues(this, pos, size, element_start, element_size);
            assert(m_pCues);  //TODO
        }
        else if (id == 0x0549A966)  //SegmentInfo ID
        {
            assert(m_pInfo == NULL);

            m_pInfo = new SegmentInfo(this,
                                      pos,
                                      size,
                                      element_start,
                                      element_size);
            assert(m_pInfo);
        }
        else if (id == 0x0654AE6B)  //Tracks ID
        {
            assert(m_pTracks == NULL);

            m_pTracks = new Tracks(this,
                                   pos,
                                   size,
                                   element_start,
                                   element_size);
            assert(m_pTracks);  //TODO
        }

        m_pos = pos + size;  //consume payload
    }

    if (m_pInfo == NULL)
        return E_FILE_FORMAT_INVALID;  //TODO: ignore this case?

    if (m_pTracks == NULL)
        return E_FILE_FORMAT_INVALID;

    if (m_clusters == NULL)  //TODO: ignore this case?
        return E_FILE_FORMAT_INVALID;

    return 0;
}


#if 0
void Segment::ParseSeekHead(long long start, long long size_)
{
    long long pos = start;
    const long long stop = start + size_;

    while (pos < stop)
    {
        long len;

        const long long id = ReadUInt(m_pReader, pos, len);
        assert(id >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume ID

        const long long size = ReadUInt(m_pReader, pos, len);
        assert(size >= 0);
        assert((pos + len) <= stop);

        pos += len;  //consume Size field
        assert((pos + size) <= stop);

        if (id == 0x0DBB)  //SeekEntry ID
            ParseSeekEntry(pos, size);

        pos += size;  //consume payload
        assert(pos <= stop);
    }

    assert(pos == stop);
}
#else
SeekHead::SeekHead(
    Segment* pSegment,
    long long start,
    long long size_,
    long long element_start,
    long long element_size) :
    m_pSegment(pSegment),
    m_start(start),
    m_size(size_),
    m_element_start(element_start),
    m_element_size(element_size),
    m_entries(0),
    m_count(0)
{
    long long pos = start;
    const long long stop = start + size_;

    IMkvReader* const pReader = m_pSegment->m_pReader;

    //first count the seek head entries

    int count = 0;

    while (pos < stop)
    {
        long len;

        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume ID

        const long long size = ReadUInt(pReader, pos, len);
        assert(size >= 0);
        assert((pos + len) <= stop);

        pos += len;  //consume Size field
        assert((pos + size) <= stop);

        if (id == 0x0DBB)  //SeekEntry ID
            ++count;

        pos += size;  //consume payload
        assert(pos <= stop);
    }

    assert(pos == stop);

    if (count <= 0)
        return;  //nothing else for us to do

    m_entries = new (std::nothrow) Entry[count];
    assert(m_entries);  //TODO

    //now parse the entries

    Entry* pEntry = m_entries;
    pos = start;

    while (pos < stop)
    {
        long len;

        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume ID

        const long long size = ReadUInt(pReader, pos, len);
        assert(size >= 0);
        assert((pos + len) <= stop);

        pos += len;  //consume Size field
        assert((pos + size) <= stop);

        if (id == 0x0DBB)  //SeekEntry ID
            ParseEntry(pReader, pos, size, pEntry);

        pos += size;  //consume payload
        assert(pos <= stop);
    }

    assert(pos == stop);

    const ptrdiff_t count_ = ptrdiff_t(pEntry - m_entries);
    assert(count_ >= 0);
    assert(count_ <= count);

    m_count = static_cast<int>(count_);
}

SeekHead::~SeekHead()
{
    delete[] m_entries;
}

int SeekHead::GetCount() const
{
    return m_count;
}

const SeekHead::Entry* SeekHead::GetEntry(int idx) const
{
    if (idx < 0)
        return 0;

    if (idx >= m_count)
        return 0;

    return m_entries + idx;
}
#endif


#if 0
void Segment::ParseCues(long long off)
{
    if (m_pCues)
        return;

    //odbgstream os;
    //os << "Segment::ParseCues (begin)" << endl;

    long long pos = m_start + off;
    const long long element_start = pos;
    const long long stop = m_start + m_size;

    long len;

    long long result = GetUIntLength(m_pReader, pos, len);
    assert(result == 0);
    assert((pos + len) <= stop);

    const long long idpos = pos;

    const long long id = ReadUInt(m_pReader, idpos, len);
    assert(id == 0x0C53BB6B);  //Cues ID

    pos += len;  //consume ID
    assert(pos < stop);

    //Read Size

    result = GetUIntLength(m_pReader, pos, len);
    assert(result == 0);
    assert((pos + len) <= stop);

    const long long size = ReadUInt(m_pReader, pos, len);
    assert(size >= 0);

    pos += len;  //consume length of size of element
    assert((pos + size) <= stop);

    const long long element_size = size + pos - element_start;

    //Pos now points to start of payload

    m_pCues = new Cues(this, pos, size, element_start, element_size);
    assert(m_pCues);  //TODO

    //os << "Segment::ParseCues (end)" << endl;
}
#else
long Segment::ParseCues(
    long long off,
    long long& pos,
    long& len)
{
    if (m_pCues)
        return 0;  //success

    if (off < 0)
        return -1;

    long long total, avail;

    const int status = m_pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    pos = m_start + off;

    if ((total < 0) || (pos >= total))
        return 1;  //don't bother parsing cues

    const long long element_start = pos;
    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;

    if ((pos + 1) > avail)
    {
        len = 1;
        return E_BUFFER_NOT_FULL;
    }

    long long result = GetUIntLength(m_pReader, pos, len);

    if (result < 0)  //error
        return static_cast<long>(result);

    if (result > 0) //underflow (weird)
    {
        len = 1;
        return E_BUFFER_NOT_FULL;
    }

    if ((segment_stop >= 0) && ((pos + len) > segment_stop))
        return E_FILE_FORMAT_INVALID;

    if ((pos + len) > avail)
        return E_BUFFER_NOT_FULL;

    const long long idpos = pos;

    const long long id = ReadUInt(m_pReader, idpos, len);

    if (id != 0x0C53BB6B)  //Cues ID
        return E_FILE_FORMAT_INVALID;

    pos += len;  //consume ID
    assert((segment_stop < 0) || (pos <= segment_stop));

    //Read Size

    if ((pos + 1) > avail)
    {
        len = 1;
        return E_BUFFER_NOT_FULL;
    }

    result = GetUIntLength(m_pReader, pos, len);

    if (result < 0)  //error
        return static_cast<long>(result);

    if (result > 0) //underflow (weird)
    {
        len = 1;
        return E_BUFFER_NOT_FULL;
    }

    if ((segment_stop >= 0) && ((pos + len) > segment_stop))
        return E_FILE_FORMAT_INVALID;

    if ((pos + len) > avail)
        return E_BUFFER_NOT_FULL;

    const long long size = ReadUInt(m_pReader, pos, len);

    if (size < 0)  //error
        return static_cast<long>(size);

    if (size == 0)  //weird, although technically not illegal
        return 1;   //done

    pos += len;  //consume length of size of element
    assert((segment_stop < 0) || (pos <= segment_stop));

    //Pos now points to start of payload

    const long long element_stop = pos + size;

    if ((segment_stop >= 0) && (element_stop > segment_stop))
        return E_FILE_FORMAT_INVALID;

    if ((total >= 0) && (element_stop > total))
        return 1;  //don't bother parsing anymore

    len = static_cast<long>(size);

    if (element_stop > avail)
        return E_BUFFER_NOT_FULL;

    const long long element_size = element_stop - element_start;

    m_pCues = new (std::nothrow) Cues(
                                    this,
                                    pos,
                                    size,
                                    element_start,
                                    element_size);
    assert(m_pCues);  //TODO

    return 0;  //success
}
#endif


#if 0
void Segment::ParseSeekEntry(
    long long start,
    long long size_)
{
    long long pos = start;

    const long long stop = start + size_;

    long len;

    const long long seekIdId = ReadUInt(m_pReader, pos, len);
    //seekIdId;
    assert(seekIdId == 0x13AB);  //SeekID ID
    assert((pos + len) <= stop);

    pos += len;  //consume id

    const long long seekIdSize = ReadUInt(m_pReader, pos, len);
    assert(seekIdSize >= 0);
    assert((pos + len) <= stop);

    pos += len;  //consume size

    const long long seekId = ReadUInt(m_pReader, pos, len);  //payload
    assert(seekId >= 0);
    assert(len == seekIdSize);
    assert((pos + len) <= stop);

    pos += seekIdSize;  //consume payload

    const long long seekPosId = ReadUInt(m_pReader, pos, len);
    //seekPosId;
    assert(seekPosId == 0x13AC);  //SeekPos ID
    assert((pos + len) <= stop);

    pos += len;  //consume id

    const long long seekPosSize = ReadUInt(m_pReader, pos, len);
    assert(seekPosSize >= 0);
    assert((pos + len) <= stop);

    pos += len;  //consume size
    assert((pos + seekPosSize) <= stop);

    const long long seekOff = UnserializeUInt(m_pReader, pos, seekPosSize);
    assert(seekOff >= 0);
    assert(seekOff < m_size);

    pos += seekPosSize;  //consume payload
    assert(pos == stop);

    const long long seekPos = m_start + seekOff;
    assert(seekPos < (m_start + m_size));

    if (seekId == 0x0C53BB6B)  //Cues ID
        ParseCues(seekOff);
}
#else
void SeekHead::ParseEntry(
    IMkvReader* pReader,
    long long start,
    long long size_,
    Entry*& pEntry)
{
    long long pos = start;
    const long long stop = start + size_;

    long len;

    //parse the container for the level-1 element ID

    const long long seekIdId = ReadUInt(pReader, pos, len);
    //seekIdId;

    if (seekIdId != 0x13AB)  //SeekID ID
        return;

    if ((pos + len) > stop)
        return;

    pos += len;  //consume SeekID id

    const long long seekIdSize = ReadUInt(pReader, pos, len);

    if (seekIdSize <= 0)
        return;

    if ((pos + len) > stop)
        return;

    pos += len;  //consume size of field

    if ((pos + seekIdSize) > stop)
        return;

    //TODO: it's not clear whether this is correct
    //It seems as if the payload here is "binary" which
    //means the value of the ID should be unserialized,
    //not parsed as an uint.
    //
    pEntry->id = ReadUInt(pReader, pos, len);  //payload

    if (pEntry->id <= 0)
        return;

    if (len != seekIdSize)
        return;

    pos += seekIdSize;  //consume SeekID payload

    const long long seekPosId = ReadUInt(pReader, pos, len);

    if (seekPosId != 0x13AC)  //SeekPos ID
        return;

    if ((pos + len) > stop)
        return;

    pos += len;  //consume id

    const long long seekPosSize = ReadUInt(pReader, pos, len);

    if (seekPosSize <= 0)
        return;

    if ((pos + len) > stop)
        return;

    pos += len;  //consume size

    if ((pos + seekPosSize) > stop)
        return;

    pEntry->pos = UnserializeUInt(pReader, pos, seekPosSize);

    if (pEntry->pos < 0)
        return;

    pos += seekPosSize;  //consume payload

    if (pos != stop)
        return;

    ++pEntry;  //success
}
#endif


Cues::Cues(
    Segment* pSegment,
    long long start_,
    long long size_,
    long long element_start,
    long long element_size) :
    m_pSegment(pSegment),
    m_start(start_),
    m_size(size_),
    m_cue_points(NULL),
    m_count(0),
    m_preload_count(0),
    m_pos(start_),
    m_element_start(element_start),
    m_element_size(element_size)
{
}


Cues::~Cues()
{
    const long n = m_count + m_preload_count;

    CuePoint** p = m_cue_points;
    CuePoint** const q = p + n;

    while (p != q)
    {
        CuePoint* const pCP = *p++;
        assert(pCP);

        delete pCP;
    }

    delete[] m_cue_points;
}


long Cues::GetCount() const
{
    if (m_cue_points == NULL)
        return -1;

    return m_count;  //TODO: really ignore preload count?
}


bool Cues::DoneParsing() const
{
    const long long stop = m_start + m_size;
    return (m_pos >= stop);
}


void Cues::Init() const
{
    if (m_cue_points)
        return;

    assert(m_count == 0);
    assert(m_preload_count == 0);

    IMkvReader* const pReader = m_pSegment->m_pReader;

    const long long stop = m_start + m_size;
    long long pos = m_start;

    long cue_points_size = 0;

    while (pos < stop)
    {
        const long long idpos = pos;

        long len;

        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume ID

        const long long size = ReadUInt(pReader, pos, len);
        assert(size >= 0);
        assert((pos + len) <= stop);

        pos += len;  //consume Size field
        assert((pos + size) <= stop);

        if (id == 0x3B)  //CuePoint ID
            PreloadCuePoint(cue_points_size, idpos);

        pos += size;  //consume payload
        assert(pos <= stop);
    }
}


void Cues::PreloadCuePoint(
    long& cue_points_size,
    long long pos) const
{
    assert(m_count == 0);

    if (m_preload_count >= cue_points_size)
    {
        long n;

        if (cue_points_size > 0)
            n = 2 * cue_points_size;
        else
        {
            const SegmentInfo* const pInfo = m_pSegment->GetInfo();

            if (pInfo == NULL)
                n = 2048;
            else
            {
                const long long ns = pInfo->GetDuration();

                if (ns <= 0)
                    n = 2048;
                else
                {
                    const long long sec = (ns + 999999999LL) / 1000000000LL;
                    n = static_cast<long>(sec);
                }
            }
        }

        CuePoint** const qq = new CuePoint*[n];
        CuePoint** q = qq;  //beginning of target

        CuePoint** p = m_cue_points;                //beginning of source
        CuePoint** const pp = p + m_preload_count;  //end of source

        while (p != pp)
            *q++ = *p++;

        delete[] m_cue_points;

        m_cue_points = qq;
        cue_points_size = n;
    }

    CuePoint* const pCP = new CuePoint(m_preload_count, pos);
    m_cue_points[m_preload_count++] = pCP;
}


bool Cues::LoadCuePoint() const
{
    //odbgstream os;
    //os << "Cues::LoadCuePoint" << endl;

    const long long stop = m_start + m_size;

    if (m_pos >= stop)
        return false;  //nothing else to do

    Init();

    IMkvReader* const pReader = m_pSegment->m_pReader;

    while (m_pos < stop)
    {
        const long long idpos = m_pos;

        long len;

        const long long id = ReadUInt(pReader, m_pos, len);
        assert(id >= 0);  //TODO
        assert((m_pos + len) <= stop);

        m_pos += len;  //consume ID

        const long long size = ReadUInt(pReader, m_pos, len);
        assert(size >= 0);
        assert((m_pos + len) <= stop);

        m_pos += len;  //consume Size field
        assert((m_pos + size) <= stop);

        if (id != 0x3B)  //CuePoint ID
        {
            m_pos += size;  //consume payload
            assert(m_pos <= stop);

            continue;
        }

        assert(m_preload_count > 0);

        CuePoint* const pCP = m_cue_points[m_count];
        assert(pCP);
        assert((pCP->GetTimeCode() >= 0) || (-pCP->GetTimeCode() == idpos));

        pCP->Load(pReader);
        ++m_count;
        --m_preload_count;

        m_pos += size;  //consume payload
        assert(m_pos <= stop);

        break;
    }

    return (m_pos < stop);
}


bool Cues::Find(
    long long time_ns,
    const Track* pTrack,
    const CuePoint*& pCP,
    const CuePoint::TrackPosition*& pTP) const
{
    assert(time_ns >= 0);
    assert(pTrack);

#if 0
    LoadCuePoint();  //establish invariant

    assert(m_cue_points);
    assert(m_count > 0);

    CuePoint** const ii = m_cue_points;
    CuePoint** i = ii;

    CuePoint** const jj = ii + m_count + m_preload_count;
    CuePoint** j = jj;

    pCP = *i;
    assert(pCP);

    if (time_ns <= pCP->GetTime(m_pSegment))
    {
        pTP = pCP->Find(pTrack);
        return (pTP != NULL);
    }

    IMkvReader* const pReader = m_pSegment->m_pReader;

    while (i < j)
    {
        //INVARIANT:
        //[ii, i) <= time_ns
        //[i, j)  ?
        //[j, jj) > time_ns

        CuePoint** const k = i + (j - i) / 2;
        assert(k < jj);

        CuePoint* const pCP = *k;
        assert(pCP);

        pCP->Load(pReader);

        const long long t = pCP->GetTime(m_pSegment);

        if (t <= time_ns)
            i = k + 1;
        else
            j = k;

        assert(i <= j);
    }

    assert(i == j);
    assert(i <= jj);
    assert(i > ii);

    pCP = *--i;
    assert(pCP);
    assert(pCP->GetTime(m_pSegment) <= time_ns);
#else
    if (m_cue_points == NULL)
        return false;

    if (m_count == 0)
        return false;

    CuePoint** const ii = m_cue_points;
    CuePoint** i = ii;

    CuePoint** const jj = ii + m_count;
    CuePoint** j = jj;

    pCP = *i;
    assert(pCP);

    if (time_ns <= pCP->GetTime(m_pSegment))
    {
        pTP = pCP->Find(pTrack);
        return (pTP != NULL);
    }

    while (i < j)
    {
        //INVARIANT:
        //[ii, i) <= time_ns
        //[i, j)  ?
        //[j, jj) > time_ns

        CuePoint** const k = i + (j - i) / 2;
        assert(k < jj);

        CuePoint* const pCP = *k;
        assert(pCP);

        const long long t = pCP->GetTime(m_pSegment);

        if (t <= time_ns)
            i = k + 1;
        else
            j = k;

        assert(i <= j);
    }

    assert(i == j);
    assert(i <= jj);
    assert(i > ii);

    pCP = *--i;
    assert(pCP);
    assert(pCP->GetTime(m_pSegment) <= time_ns);
#endif

    //TODO: here and elsewhere, it's probably not correct to search
    //for the cue point with this time, and then search for a matching
    //track.  In principle, the matching track could be on some earlier
    //cue point, and with our current algorithm, we'd miss it.  To make
    //this bullet-proof, we'd need to create a secondary structure,
    //with a list of cue points that apply to a track, and then search
    //that track-based structure for a matching cue point.

    pTP = pCP->Find(pTrack);
    return (pTP != NULL);
}


#if 0
bool Cues::FindNext(
    long long time_ns,
    const Track* pTrack,
    const CuePoint*& pCP,
    const CuePoint::TrackPosition*& pTP) const
{
    pCP = 0;
    pTP = 0;

    if (m_count == 0)
        return false;

    assert(m_cue_points);

    const CuePoint* const* const ii = m_cue_points;
    const CuePoint* const* i = ii;

    const CuePoint* const* const jj = ii + m_count;
    const CuePoint* const* j = jj;

    while (i < j)
    {
        //INVARIANT:
        //[ii, i) <= time_ns
        //[i, j)  ?
        //[j, jj) > time_ns

        const CuePoint* const* const k = i + (j - i) / 2;
        assert(k < jj);

        pCP = *k;
        assert(pCP);

        const long long t = pCP->GetTime(m_pSegment);

        if (t <= time_ns)
            i = k + 1;
        else
            j = k;

        assert(i <= j);
    }

    assert(i == j);
    assert(i <= jj);

    if (i >= jj)  //time_ns is greater than max cue point
        return false;

    pCP = *i;
    assert(pCP);
    assert(pCP->GetTime(m_pSegment) > time_ns);

    pTP = pCP->Find(pTrack);
    return (pTP != NULL);
}
#endif


const CuePoint* Cues::GetFirst() const
{
    if (m_cue_points == NULL)
        return NULL;

    if (m_count == 0)
        return NULL;

#if 0
    LoadCuePoint();  //init cues

    const size_t count = m_count + m_preload_count;

    if (count == 0)  //weird
        return NULL;
#endif

    CuePoint* const* const pp = m_cue_points;
    assert(pp);

    CuePoint* const pCP = pp[0];
    assert(pCP);
    assert(pCP->GetTimeCode() >= 0);

    return pCP;
}


const CuePoint* Cues::GetLast() const
{
    if (m_cue_points == NULL)
        return NULL;

    if (m_count <= 0)
        return NULL;

#if 0
    LoadCuePoint();  //init cues

    const size_t count = m_count + m_preload_count;

    if (count == 0)  //weird
        return NULL;

    const size_t index = count - 1;

    CuePoint* const* const pp = m_cue_points;
    assert(pp);

    CuePoint* const pCP = pp[index];
    assert(pCP);

    pCP->Load(m_pSegment->m_pReader);
    assert(pCP->GetTimeCode() >= 0);
#else
    const long index = m_count - 1;

    CuePoint* const* const pp = m_cue_points;
    assert(pp);

    CuePoint* const pCP = pp[index];
    assert(pCP);
    assert(pCP->GetTimeCode() >= 0);
#endif

    return pCP;
}


const CuePoint* Cues::GetNext(const CuePoint* pCurr) const
{
    if (pCurr == NULL)
        return NULL;

    assert(pCurr->GetTimeCode() >= 0);
    assert(m_cue_points);
    assert(m_count >= 1);

#if 0
    const size_t count = m_count + m_preload_count;

    size_t index = pCurr->m_index;
    assert(index < count);

    CuePoint* const* const pp = m_cue_points;
    assert(pp);
    assert(pp[index] == pCurr);

    ++index;

    if (index >= count)
        return NULL;

    CuePoint* const pNext = pp[index];
    assert(pNext);

    pNext->Load(m_pSegment->m_pReader);
#else
    long index = pCurr->m_index;
    assert(index < m_count);

    CuePoint* const* const pp = m_cue_points;
    assert(pp);
    assert(pp[index] == pCurr);

    ++index;

    if (index >= m_count)
        return NULL;

    CuePoint* const pNext = pp[index];
    assert(pNext);
    assert(pNext->GetTimeCode() >= 0);
#endif

    return pNext;
}


const BlockEntry* Cues::GetBlock(
    const CuePoint* pCP,
    const CuePoint::TrackPosition* pTP) const
{
    if (pCP == NULL)
        return NULL;

    if (pTP == NULL)
        return NULL;

    return m_pSegment->GetBlock(*pCP, *pTP);
}


const BlockEntry* Segment::GetBlock(
    const CuePoint& cp,
    const CuePoint::TrackPosition& tp)
{
    Cluster** const ii = m_clusters;
    Cluster** i = ii;

    const long count = m_clusterCount + m_clusterPreloadCount;

    Cluster** const jj = ii + count;
    Cluster** j = jj;

    while (i < j)
    {
        //INVARIANT:
        //[ii, i) < pTP->m_pos
        //[i, j) ?
        //[j, jj)  > pTP->m_pos

        Cluster** const k = i + (j - i) / 2;
        assert(k < jj);

        Cluster* const pCluster = *k;
        assert(pCluster);

        //const long long pos_ = pCluster->m_pos;
        //assert(pos_);
        //const long long pos = pos_ * ((pos_ < 0) ? -1 : 1);

        const long long pos = pCluster->GetPosition();
        assert(pos >= 0);

        if (pos < tp.m_pos)
            i = k + 1;
        else if (pos > tp.m_pos)
            j = k;
        else
            return pCluster->GetEntry(cp, tp);
    }

    assert(i == j);
    //assert(Cluster::HasBlockEntries(this, tp.m_pos));

    Cluster* const pCluster = Cluster::Create(this, -1, tp.m_pos); //, -1);
    assert(pCluster);

    const ptrdiff_t idx = i - m_clusters;

    PreloadCluster(pCluster, idx);
    assert(m_clusters);
    assert(m_clusterPreloadCount > 0);
    assert(m_clusters[idx] == pCluster);

    return pCluster->GetEntry(cp, tp);
}


const Cluster* Segment::FindOrPreloadCluster(long long requested_pos)
{
    if (requested_pos < 0)
        return 0;

    Cluster** const ii = m_clusters;
    Cluster** i = ii;

    const long count = m_clusterCount + m_clusterPreloadCount;

    Cluster** const jj = ii + count;
    Cluster** j = jj;

    while (i < j)
    {
        //INVARIANT:
        //[ii, i) < pTP->m_pos
        //[i, j) ?
        //[j, jj)  > pTP->m_pos

        Cluster** const k = i + (j - i) / 2;
        assert(k < jj);

        Cluster* const pCluster = *k;
        assert(pCluster);

        //const long long pos_ = pCluster->m_pos;
        //assert(pos_);
        //const long long pos = pos_ * ((pos_ < 0) ? -1 : 1);

        const long long pos = pCluster->GetPosition();
        assert(pos >= 0);

        if (pos < requested_pos)
            i = k + 1;
        else if (pos > requested_pos)
            j = k;
        else
            return pCluster;
    }

    assert(i == j);
    //assert(Cluster::HasBlockEntries(this, tp.m_pos));

    Cluster* const pCluster = Cluster::Create(
                                this,
                                -1,
                                requested_pos);
                                //-1);
    assert(pCluster);

    const ptrdiff_t idx = i - m_clusters;

    PreloadCluster(pCluster, idx);
    assert(m_clusters);
    assert(m_clusterPreloadCount > 0);
    assert(m_clusters[idx] == pCluster);

    return pCluster;
}


CuePoint::CuePoint(long idx, long long pos) :
    m_element_start(0),
    m_element_size(0),
    m_index(idx),
    m_timecode(-1 * pos),
    m_track_positions(NULL),
    m_track_positions_count(0)
{
    assert(pos > 0);
}


CuePoint::~CuePoint()
{
    delete[] m_track_positions;
}


void CuePoint::Load(IMkvReader* pReader)
{
    //odbgstream os;
    //os << "CuePoint::Load(begin): timecode=" << m_timecode << endl;

    if (m_timecode >= 0)  //already loaded
        return;

    assert(m_track_positions == NULL);
    assert(m_track_positions_count == 0);

    long long pos_ = -m_timecode;
    const long long element_start = pos_;

    long long stop;

    {
        long len;

        const long long id = ReadUInt(pReader, pos_, len);
        assert(id == 0x3B);  //CuePoint ID
        //assert((pos + len) <= stop);

        pos_ += len;  //consume ID

        const long long size = ReadUInt(pReader, pos_, len);
        assert(size >= 0);
        //assert((pos + len) <= stop);

        pos_ += len;  //consume Size field
        //assert((pos + size) <= stop);

        //pos_ now points to start of payload

        stop = pos_ + size;
    }

    const long long element_size = stop - element_start;

    long long pos = pos_;

    //First count number of track positions

    while (pos < stop)
    {
        long len;

        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume ID

        const long long size = ReadUInt(pReader, pos, len);
        assert(size >= 0);
        assert((pos + len) <= stop);

        pos += len;  //consume Size field
        assert((pos + size) <= stop);

        if (id == 0x33)  //CueTime ID
            m_timecode = UnserializeUInt(pReader, pos, size);

        else if (id == 0x37) //CueTrackPosition(s) ID
            ++m_track_positions_count;

        pos += size;  //consume payload
        assert(pos <= stop);
    }

    assert(m_timecode >= 0);
    assert(m_track_positions_count > 0);

    //os << "CuePoint::Load(cont'd): idpos=" << idpos
    //   << " timecode=" << m_timecode
    //   << endl;

    m_track_positions = new TrackPosition[m_track_positions_count];

    //Now parse track positions

    TrackPosition* p = m_track_positions;
    pos = pos_;

    while (pos < stop)
    {
        long len;

        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume ID

        const long long size = ReadUInt(pReader, pos, len);
        assert(size >= 0);
        assert((pos + len) <= stop);

        pos += len;  //consume Size field
        assert((pos + size) <= stop);

        if (id == 0x37) //CueTrackPosition(s) ID
        {
            TrackPosition& tp = *p++;
            tp.Parse(pReader, pos, size);
        }

        pos += size;  //consume payload
        assert(pos <= stop);
    }

    assert(size_t(p - m_track_positions) == m_track_positions_count);

    m_element_start = element_start;
    m_element_size = element_size;
}



void CuePoint::TrackPosition::Parse(
    IMkvReader* pReader,
    long long start_,
    long long size_)
{
    const long long stop = start_ + size_;
    long long pos = start_;

    m_track = -1;
    m_pos = -1;
    m_block = 1;  //default

    while (pos < stop)
    {
        long len;

        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume ID

        const long long size = ReadUInt(pReader, pos, len);
        assert(size >= 0);
        assert((pos + len) <= stop);

        pos += len;  //consume Size field
        assert((pos + size) <= stop);

        if (id == 0x77)  //CueTrack ID
            m_track = UnserializeUInt(pReader, pos, size);

        else if (id == 0x71)  //CueClusterPos ID
            m_pos = UnserializeUInt(pReader, pos, size);

        else if (id == 0x1378)  //CueBlockNumber
            m_block = UnserializeUInt(pReader, pos, size);

        pos += size;  //consume payload
        assert(pos <= stop);
    }

    assert(m_pos >= 0);
    assert(m_track > 0);
    //assert(m_block > 0);
}


const CuePoint::TrackPosition* CuePoint::Find(const Track* pTrack) const
{
    assert(pTrack);

    const long long n = pTrack->GetNumber();

    const TrackPosition* i = m_track_positions;
    const TrackPosition* const j = i + m_track_positions_count;

    while (i != j)
    {
        const TrackPosition& p = *i++;

        if (p.m_track == n)
            return &p;
    }

    return NULL;  //no matching track number found
}


long long CuePoint::GetTimeCode() const
{
    return m_timecode;
}

long long CuePoint::GetTime(const Segment* pSegment) const
{
    assert(pSegment);
    assert(m_timecode >= 0);

    const SegmentInfo* const pInfo = pSegment->GetInfo();
    assert(pInfo);

    const long long scale = pInfo->GetTimeCodeScale();
    assert(scale >= 1);

    const long long time = scale * m_timecode;

    return time;
}


long long Segment::Unparsed() const
{
    if (m_size < 0)
        return LLONG_MAX;

    const long long stop = m_start + m_size;

    const long long result = stop - m_pos;
    assert(result >= 0);

    return result;
}


const Cluster* Segment::GetFirst() const
{
    if ((m_clusters == NULL) || (m_clusterCount <= 0))
       return &m_eos;

    Cluster* const pCluster = m_clusters[0];
    assert(pCluster);

    return pCluster;
}


const Cluster* Segment::GetLast() const
{
    if ((m_clusters == NULL) || (m_clusterCount <= 0))
        return &m_eos;

    const long idx = m_clusterCount - 1;

    Cluster* const pCluster = m_clusters[idx];
    assert(pCluster);

    return pCluster;
}


unsigned long Segment::GetCount() const
{
    return m_clusterCount;
}


const Cluster* Segment::GetNext(const Cluster* pCurr)
{
    assert(pCurr);
    assert(pCurr != &m_eos);
    assert(m_clusters);

    long idx =  pCurr->m_index;

    if (idx >= 0)
    {
        assert(m_clusterCount > 0);
        assert(idx < m_clusterCount);
        assert(pCurr == m_clusters[idx]);

        ++idx;

        if (idx >= m_clusterCount)
            return &m_eos;  //caller will LoadCluster as desired

        Cluster* const pNext = m_clusters[idx];
        assert(pNext);
        assert(pNext->m_index >= 0);
        assert(pNext->m_index == idx);

        return pNext;
    }

    assert(m_clusterPreloadCount > 0);

    //const long long off_ = pCurr->m_pos;
    //const long long off = off_ * ((off_ < 0) ? -1 : 1);
    //long long pos = m_start + off;

    long long pos = pCurr->m_element_start;

    assert(m_size >= 0);  //TODO
    const long long stop = m_start + m_size;  //end of segment

    {
        long len;

        long long result = GetUIntLength(m_pReader, pos, len);
        assert(result == 0);  //TODO
        assert((pos + len) <= stop);  //TODO

        const long long id = ReadUInt(m_pReader, pos, len);
        assert(id == 0x0F43B675);  //Cluster ID   //TODO

        pos += len;  //consume ID

        //Read Size
        result = GetUIntLength(m_pReader, pos, len);
        assert(result == 0);  //TODO
        assert((pos + len) <= stop);  //TODO

        const long long size = ReadUInt(m_pReader, pos, len);
        assert(size > 0);  //TODO
        //assert((pCurr->m_size <= 0) || (pCurr->m_size == size));

        pos += len;  //consume length of size of element
        assert((pos + size) <= stop);  //TODO

        //Pos now points to start of payload

        pos += size;  //consume payload
    }

    long long off_next = 0;
    //long long element_start_next = 0;
    long long element_size_next = 0;

    while (pos < stop)
    {
        long len;

        long long result = GetUIntLength(m_pReader, pos, len);
        assert(result == 0);  //TODO
        assert((pos + len) <= stop);  //TODO

        const long long idpos = pos;  //pos of next (potential) cluster

        const long long id = ReadUInt(m_pReader, idpos, len);
        assert(id > 0);  //TODO

        pos += len;  //consume ID

        //Read Size
        result = GetUIntLength(m_pReader, pos, len);
        assert(result == 0);  //TODO
        assert((pos + len) <= stop);  //TODO

        const long long size = ReadUInt(m_pReader, pos, len);
        assert(size >= 0);  //TODO

        pos += len;  //consume length of size of element
        assert((pos + size) <= stop);  //TODO

        const long long element_size = size + pos - idpos;

        //Pos now points to start of payload

        if (size == 0)  //weird
            continue;

        if (id == 0x0F43B675)  //Cluster ID
        {
            const long long off_next_ = idpos - m_start;

            long long pos_;
            long len_;

            const long status = Cluster::HasBlockEntries(
                                    this,
                                    off_next_,
                                    pos_,
                                    len_);

            assert(status >= 0);

            if (status > 0)
            {
                off_next = off_next_;
                //element_start_next = idpos;
                element_size_next = element_size;
                break;
            }
        }

        pos += size;  //consume payload
    }

    if (off_next <= 0)
        return 0;

    Cluster** const ii = m_clusters + m_clusterCount;
    Cluster** i = ii;

    Cluster** const jj = ii + m_clusterPreloadCount;
    Cluster** j = jj;

    while (i < j)
    {
        //INVARIANT:
        //[0, i) < pos_next
        //[i, j) ?
        //[j, jj)  > pos_next

        Cluster** const k = i + (j - i) / 2;
        assert(k < jj);

        Cluster* const pNext = *k;
        assert(pNext);
        assert(pNext->m_index < 0);

        //const long long pos_ = pNext->m_pos;
        //assert(pos_);
        //pos = pos_ * ((pos_ < 0) ? -1 : 1);

        pos = pNext->GetPosition();

        if (pos < off_next)
            i = k + 1;
        else if (pos > off_next)
            j = k;
        else
            return pNext;
    }

    assert(i == j);

    Cluster* const pNext = Cluster::Create(this,
                                          -1,
                                          off_next);
                                          //element_size_next);
    assert(pNext);

    const ptrdiff_t idx_next = i - m_clusters;  //insertion position

    PreloadCluster(pNext, idx_next);
    assert(m_clusters);
    assert(idx_next < m_clusterSize);
    assert(m_clusters[idx_next] == pNext);

    return pNext;
}


long Segment::ParseNext(
    const Cluster* pCurr,
    const Cluster*& pResult,
    long long& pos,
    long& len)
{
    assert(pCurr);
    assert(!pCurr->EOS());
    assert(m_clusters);

    pResult = 0;

    if (pCurr->m_index >= 0)  //loaded (not merely preloaded)
    {
        assert(m_clusters[pCurr->m_index] == pCurr);

        const long next_idx = pCurr->m_index + 1;

        if (next_idx < m_clusterCount)
        {
            pResult = m_clusters[next_idx];
            return 0;  //success
        }

        //curr cluster is last among loaded

        const long result = LoadCluster(pos, len);

        if (result < 0)  //error or underflow
            return result;

        if (result > 0)  //no more clusters
        {
            //pResult = &m_eos;
            return 1;
        }

        pResult = GetLast();
        return 0;  //success
    }

    assert(m_pos > 0);

    long long total, avail;

    long status = m_pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;

    //interrogate curr cluster

    pos = pCurr->m_element_start;

    if (pCurr->m_element_size >= 0)
        pos += pCurr->m_element_size;
    else
    {
        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long id = ReadUInt(m_pReader, pos, len);

        if (id != 0x0F43B675)  //weird: not Cluster ID
            return -1;

        pos += len;  //consume ID

        //Read Size

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(m_pReader, pos, len);

        if (size < 0) //error
            return static_cast<long>(size);

        pos += len;  //consume size field

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size == unknown_size)          //TODO: should never happen
            return E_FILE_FORMAT_INVALID;  //TODO: resolve this

        //assert((pCurr->m_size <= 0) || (pCurr->m_size == size));

        if ((segment_stop >= 0) && ((pos + size) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        //Pos now points to start of payload

        pos += size;  //consume payload (that is, the current cluster)
        assert((segment_stop < 0) || (pos <= segment_stop));

        //By consuming the payload, we are assuming that the curr
        //cluster isn't interesting.  That is, we don't bother checking
        //whether the payload of the curr cluster is less than what
        //happens to be available (obtained via IMkvReader::Length).
        //Presumably the caller has already dispensed with the current
        //cluster, and really does want the next cluster.
    }

    //pos now points to just beyond the last fully-loaded cluster

    for (;;)
    {
        const long status = DoParseNext(pResult, pos, len);

        if (status <= 1)
            return status;
    }
}


long Segment::DoParseNext(
    const Cluster*& pResult,
    long long& pos,
    long& len)
{
    long long total, avail;

    long status = m_pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    const long long segment_stop = (m_size < 0) ? -1 : m_start + m_size;

    //Parse next cluster.  This is strictly a parsing activity.
    //Creation of a new cluster object happens later, after the
    //parsing is done.

    long long off_next = 0;
    long long cluster_size = -1;

    for (;;)
    {
        if ((total >= 0) && (pos >= total))
            return 1;  //EOF

        if ((segment_stop >= 0) && (pos >= segment_stop))
            return 1;  //EOF

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long idpos = pos;             //absolute
        const long long idoff = pos - m_start;   //relative

        const long long id = ReadUInt(m_pReader, idpos, len);  //absolute

        if (id < 0)  //error
            return static_cast<long>(id);

        if (id == 0)  //weird
            return -1;  //generic error

        pos += len;  //consume ID

        //Read Size

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(m_pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(m_pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        pos += len;  //consume length of size of element

        //Pos now points to start of payload

        if (size == 0)  //weird
            continue;

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if ((segment_stop >= 0) &&
            (size != unknown_size) &&
            ((pos + size) > segment_stop))
        {
            return E_FILE_FORMAT_INVALID;
        }

        if (id == 0x0C53BB6B)  //Cues ID
        {
            if (size == unknown_size)
                return E_FILE_FORMAT_INVALID;

            const long long element_stop = pos + size;

            if ((segment_stop >= 0) && (element_stop > segment_stop))
                return E_FILE_FORMAT_INVALID;

            const long long element_start = idpos;
            const long long element_size = element_stop - element_start;

            if (m_pCues == NULL)
            {
                m_pCues = new Cues(this,
                                    pos,
                                    size,
                                    element_start,
                                    element_size);
                assert(m_pCues);  //TODO
            }

            pos += size;  //consume payload
            assert((segment_stop < 0) || (pos <= segment_stop));

            continue;
        }

        if (id != 0x0F43B675)  //not a Cluster ID
        {
            if (size == unknown_size)
                return E_FILE_FORMAT_INVALID;

            pos += size;  //consume payload
            assert((segment_stop < 0) || (pos <= segment_stop));

            continue;
        }

#if 0 //this is commented-out to support incremental cluster parsing
        len = static_cast<long>(size);

        if (element_stop > avail)
            return E_BUFFER_NOT_FULL;
#endif

        //We have a cluster.

        off_next = idoff;

        if (size != unknown_size)
            cluster_size = size;

        break;
    }

    assert(off_next > 0);  //have cluster

    //We have parsed the next cluster.
    //We have not created a cluster object yet.  What we need
    //to do now is determine whether it has already be preloaded
    //(in which case, an object for this cluster has already been
    //created), and if not, create a new cluster object.

    Cluster** const ii = m_clusters + m_clusterCount;
    Cluster** i = ii;

    Cluster** const jj = ii + m_clusterPreloadCount;
    Cluster** j = jj;

    while (i < j)
    {
        //INVARIANT:
        //[0, i) < pos_next
        //[i, j) ?
        //[j, jj)  > pos_next

        Cluster** const k = i + (j - i) / 2;
        assert(k < jj);

        const Cluster* const pNext = *k;
        assert(pNext);
        assert(pNext->m_index < 0);

        pos = pNext->GetPosition();
        assert(pos >= 0);

        if (pos < off_next)
            i = k + 1;
        else if (pos > off_next)
            j = k;
        else
        {
            pResult = pNext;
            return 0;  //success
        }
    }

    assert(i == j);

    long long pos_;
    long len_;

    status = Cluster::HasBlockEntries(this, off_next, pos_, len_);

    if (status < 0)  //error or underflow
    {
        pos = pos_;
        len = len_;

        return status;
    }

    if (status > 0)  //means "found at least one block entry"
    {
        Cluster* const pNext = Cluster::Create(this,
                                                -1,   //preloaded
                                                off_next);
                                                //element_size);
        assert(pNext);

        const ptrdiff_t idx_next = i - m_clusters;  //insertion position

        PreloadCluster(pNext, idx_next);
        assert(m_clusters);
        assert(idx_next < m_clusterSize);
        assert(m_clusters[idx_next] == pNext);

        pResult = pNext;
        return 0;  //success
    }

    //status == 0 means "no block entries found"

    if (cluster_size < 0)  //unknown size
    {
        const long long payload_pos = pos;  //absolute pos of cluster payload

        for (;;)  //determine cluster size
        {
            if ((total >= 0) && (pos >= total))
                break;

            if ((segment_stop >= 0) && (pos >= segment_stop))
                break;  //no more clusters

            //Read ID

            if ((pos + 1) > avail)
            {
                len = 1;
                return E_BUFFER_NOT_FULL;
            }

            long long result = GetUIntLength(m_pReader, pos, len);

            if (result < 0)  //error
                return static_cast<long>(result);

            if (result > 0)  //weird
                return E_BUFFER_NOT_FULL;

            if ((segment_stop >= 0) && ((pos + len) > segment_stop))
                return E_FILE_FORMAT_INVALID;

            if ((pos + len) > avail)
                return E_BUFFER_NOT_FULL;

            const long long idpos = pos;
            const long long id = ReadUInt(m_pReader, idpos, len);

            if (id < 0)  //error (or underflow)
                return static_cast<long>(id);

            //This is the distinguished set of ID's we use to determine
            //that we have exhausted the sub-element's inside the cluster
            //whose ID we parsed earlier.

            if (id == 0x0F43B675)  //Cluster ID
                break;

            if (id == 0x0C53BB6B)  //Cues ID
                break;

            pos += len;  //consume ID (of sub-element)

            //Read Size

            if ((pos + 1) > avail)
            {
                len = 1;
                return E_BUFFER_NOT_FULL;
            }

            result = GetUIntLength(m_pReader, pos, len);

            if (result < 0)  //error
                return static_cast<long>(result);

            if (result > 0)  //weird
                return E_BUFFER_NOT_FULL;

            if ((segment_stop >= 0) && ((pos + len) > segment_stop))
                return E_FILE_FORMAT_INVALID;

            if ((pos + len) > avail)
                return E_BUFFER_NOT_FULL;

            const long long size = ReadUInt(m_pReader, pos, len);

            if (size < 0)  //error
                return static_cast<long>(size);

            pos += len;  //consume size field of element

            //pos now points to start of sub-element's payload

            if (size == 0)  //weird
                continue;

            const long long unknown_size = (1LL << (7 * len)) - 1;

            if (size == unknown_size)
                return E_FILE_FORMAT_INVALID;  //not allowed for sub-elements

            if ((segment_stop >= 0) && ((pos + size) > segment_stop))  //weird
                return E_FILE_FORMAT_INVALID;

            pos += size;  //consume payload of sub-element
            assert((segment_stop < 0) || (pos <= segment_stop));
        }  //determine cluster size

        cluster_size = pos - payload_pos;
        assert(cluster_size >= 0);  //TODO: handle cluster_size = 0

        pos = payload_pos;  //reset and re-parse original cluster
    }

    pos += cluster_size;  //consume payload
    assert((segment_stop < 0) || (pos <= segment_stop));

    return 2;             //try to find a cluster that follows next
}


const Cluster* Segment::FindCluster(long long time_ns) const
{
    if ((m_clusters == NULL) || (m_clusterCount <= 0))
        return &m_eos;

    {
        Cluster* const pCluster = m_clusters[0];
        assert(pCluster);
        assert(pCluster->m_index == 0);

        if (time_ns <= pCluster->GetTime())
            return pCluster;
    }

    //Binary search of cluster array

    long i = 0;
    long j = m_clusterCount;

    while (i < j)
    {
        //INVARIANT:
        //[0, i) <= time_ns
        //[i, j) ?
        //[j, m_clusterCount)  > time_ns

        const long k = i + (j - i) / 2;
        assert(k < m_clusterCount);

        Cluster* const pCluster = m_clusters[k];
        assert(pCluster);
        assert(pCluster->m_index == k);

        const long long t = pCluster->GetTime();

        if (t <= time_ns)
            i = k + 1;
        else
            j = k;

        assert(i <= j);
    }

    assert(i == j);
    assert(i > 0);
    assert(i <= m_clusterCount);

    const long k = i - 1;

    Cluster* const pCluster = m_clusters[k];
    assert(pCluster);
    assert(pCluster->m_index == k);
    assert(pCluster->GetTime() <= time_ns);

    return pCluster;
}


#if 0
const BlockEntry* Segment::Seek(
    long long time_ns,
    const Track* pTrack) const
{
    assert(pTrack);

    if ((m_clusters == NULL) || (m_clusterCount <= 0))
        return pTrack->GetEOS();

    Cluster** const i = m_clusters;
    assert(i);

    {
        Cluster* const pCluster = *i;
        assert(pCluster);
        assert(pCluster->m_index == 0);  //m_clusterCount > 0
        assert(pCluster->m_pSegment == this);

        if (time_ns <= pCluster->GetTime())
            return pCluster->GetEntry(pTrack);
    }

    Cluster** const j = i + m_clusterCount;

    if (pTrack->GetType() == 2)  //audio
    {
        //TODO: we could decide to use cues for this, as we do for video.
        //But we only use it for video because looking around for a keyframe
        //can get expensive.  Audio doesn't require anything special so a
        //straight cluster search is good enough (we assume).

        Cluster** lo = i;
        Cluster** hi = j;

        while (lo < hi)
        {
            //INVARIANT:
            //[i, lo) <= time_ns
            //[lo, hi) ?
            //[hi, j)  > time_ns

            Cluster** const mid = lo + (hi - lo) / 2;
            assert(mid < hi);

            Cluster* const pCluster = *mid;
            assert(pCluster);
            assert(pCluster->m_index == long(mid - m_clusters));
            assert(pCluster->m_pSegment == this);

            const long long t = pCluster->GetTime();

            if (t <= time_ns)
                lo = mid + 1;
            else
                hi = mid;

            assert(lo <= hi);
        }

        assert(lo == hi);
        assert(lo > i);
        assert(lo <= j);

        while (lo > i)
        {
            Cluster* const pCluster = *--lo;
            assert(pCluster);
            assert(pCluster->GetTime() <= time_ns);

            const BlockEntry* const pBE = pCluster->GetEntry(pTrack);

            if ((pBE != 0) && !pBE->EOS())
                return pBE;

            //landed on empty cluster (no entries)
        }

        return pTrack->GetEOS();  //weird
    }

    assert(pTrack->GetType() == 1);  //video

    Cluster** lo = i;
    Cluster** hi = j;

    while (lo < hi)
    {
        //INVARIANT:
        //[i, lo) <= time_ns
        //[lo, hi) ?
        //[hi, j)  > time_ns

        Cluster** const mid = lo + (hi - lo) / 2;
        assert(mid < hi);

        Cluster* const pCluster = *mid;
        assert(pCluster);

        const long long t = pCluster->GetTime();

        if (t <= time_ns)
            lo = mid + 1;
        else
            hi = mid;

        assert(lo <= hi);
    }

    assert(lo == hi);
    assert(lo > i);
    assert(lo <= j);

    Cluster* pCluster = *--lo;
    assert(pCluster);
    assert(pCluster->GetTime() <= time_ns);

    {
        const BlockEntry* const pBE = pCluster->GetEntry(pTrack, time_ns);

        if ((pBE != 0) && !pBE->EOS())  //found a keyframe
            return pBE;
    }

    const VideoTrack* const pVideo = static_cast<const VideoTrack*>(pTrack);

    while (lo != i)
    {
        pCluster = *--lo;
        assert(pCluster);
        assert(pCluster->GetTime() <= time_ns);

        const BlockEntry* const pBlockEntry = pCluster->GetMaxKey(pVideo);

        if ((pBlockEntry != 0) && !pBlockEntry->EOS())
            return pBlockEntry;
    }

    //weird: we're on the first cluster, but no keyframe found
    //should never happen but we must return something anyway

    return pTrack->GetEOS();
}
#endif


#if 0
bool Segment::SearchCues(
    long long time_ns,
    Track* pTrack,
    Cluster*& pCluster,
    const BlockEntry*& pBlockEntry,
    const CuePoint*& pCP,
    const CuePoint::TrackPosition*& pTP)
{
    if (pTrack->GetType() != 1)  //not video
        return false;  //TODO: for now, just handle video stream

    if (m_pCues == NULL)
        return false;

    if (!m_pCues->Find(time_ns, pTrack, pCP, pTP))
        return false;  //weird

    assert(pCP);
    assert(pTP);
    assert(pTP->m_track == pTrack->GetNumber());

    //We have the cue point and track position we want,
    //so we now need to search for the cluster having
    //the indicated position.

    return GetCluster(pCP, pTP, pCluster, pBlockEntry);
}
#endif


const Tracks* Segment::GetTracks() const
{
    return m_pTracks;
}


const SegmentInfo* Segment::GetInfo() const
{
    return m_pInfo;
}


const Cues* Segment::GetCues() const
{
    return m_pCues;
}


const SeekHead* Segment::GetSeekHead() const
{
    return m_pSeekHead;
}


long long Segment::GetDuration() const
{
    assert(m_pInfo);
    return m_pInfo->GetDuration();
}


SegmentInfo::SegmentInfo(
    Segment* pSegment,
    long long start,
    long long size_,
    long long element_start,
    long long element_size) :
    m_pSegment(pSegment),
    m_start(start),
    m_size(size_),
    m_pMuxingAppAsUTF8(NULL),
    m_pWritingAppAsUTF8(NULL),
    m_pTitleAsUTF8(NULL),
    m_element_start(element_start),
    m_element_size(element_size)
{
    IMkvReader* const pReader = m_pSegment->m_pReader;

    long long pos = start;
    const long long stop = start + size_;

    m_timecodeScale = 1000000;
    m_duration = -1;

    while (pos < stop)
    {
        if (Match(pReader, pos, 0x0AD7B1, m_timecodeScale))
            assert(m_timecodeScale > 0);

        else if (Match(pReader, pos, 0x0489, m_duration))
            assert(m_duration >= 0);

        else if (Match(pReader, pos, 0x0D80, m_pMuxingAppAsUTF8))   //[4D][80]
            assert(m_pMuxingAppAsUTF8);

        else if (Match(pReader, pos, 0x1741, m_pWritingAppAsUTF8))  //[57][41]
            assert(m_pWritingAppAsUTF8);

        else if (Match(pReader, pos, 0x3BA9, m_pTitleAsUTF8))       //[7B][A9]
            assert(m_pTitleAsUTF8);

        else
        {
            long len;

            const long long id = ReadUInt(pReader, pos, len);
            //id;
            assert(id >= 0);
            assert((pos + len) <= stop);

            pos += len;  //consume id
            assert((stop - pos) > 0);

            const long long size = ReadUInt(pReader, pos, len);
            assert(size >= 0);
            assert((pos + len) <= stop);

            pos += len + size;  //consume size and payload
            assert(pos <= stop);
        }
    }

    assert(pos == stop);
}

SegmentInfo::~SegmentInfo()
{
    if (m_pMuxingAppAsUTF8)
    {
        delete[] m_pMuxingAppAsUTF8;
        m_pMuxingAppAsUTF8 = NULL;
    }

    if (m_pWritingAppAsUTF8)
    {
        delete[] m_pWritingAppAsUTF8;
        m_pWritingAppAsUTF8 = NULL;
    }

    if (m_pTitleAsUTF8)
    {
        delete[] m_pTitleAsUTF8;
        m_pTitleAsUTF8 = NULL;
    }
}

long long SegmentInfo::GetTimeCodeScale() const
{
    return m_timecodeScale;
}


long long SegmentInfo::GetDuration() const
{
    if (m_duration < 0)
        return -1;

    assert(m_timecodeScale >= 1);

    const double dd = double(m_duration) * double(m_timecodeScale);
    const long long d = static_cast<long long>(dd);

    return d;
}

const char* SegmentInfo::GetMuxingAppAsUTF8() const
{
    return m_pMuxingAppAsUTF8;
}


const char* SegmentInfo::GetWritingAppAsUTF8() const
{
    return m_pWritingAppAsUTF8;
}

const char* SegmentInfo::GetTitleAsUTF8() const
{
    return m_pTitleAsUTF8;
}

Track::Track(
    Segment* pSegment,
    const Info& i,
    long long element_start,
    long long element_size) :
    m_pSegment(pSegment),
    m_info(i),
    m_element_start(element_start),
    m_element_size(element_size)
{
}

Track::~Track()
{
    Info& info = const_cast<Info&>(m_info);
    info.Clear();
}

Track::Info::Info():
    type(-1),
    number(-1),
    uid(ULLONG_MAX),
    nameAsUTF8(NULL),
    codecId(NULL),
    codecPrivate(NULL),
    codecPrivateSize(0),
    codecNameAsUTF8(NULL)
{
}

void Track::Info::Clear()
{
    delete[] nameAsUTF8;
    nameAsUTF8 = NULL;

    delete[] codecId;
    codecId = NULL;

    delete[] codecPrivate;
    codecPrivate = NULL;

    codecPrivateSize = 0;

    delete[] codecNameAsUTF8;
    codecNameAsUTF8 = NULL;
}

const BlockEntry* Track::GetEOS() const
{
    return &m_eos;
}

long long Track::GetType() const
{
    return m_info.type;
}

long long Track::GetNumber() const
{
    return m_info.number;
}

unsigned long long Track::GetUid() const
{
    return m_info.uid;
}

const char* Track::GetNameAsUTF8() const
{
    return m_info.nameAsUTF8;
}

const char* Track::GetCodecNameAsUTF8() const
{
    return m_info.codecNameAsUTF8;
}


const char* Track::GetCodecId() const
{
    return m_info.codecId;
}

const unsigned char* Track::GetCodecPrivate(size_t& size) const
{
    size = m_info.codecPrivateSize;
    return m_info.codecPrivate;
}


bool Track::GetLacing() const
{
    return m_info.lacing;
}


long Track::GetFirst(const BlockEntry*& pBlockEntry) const
{
    const Cluster* pCluster = m_pSegment->GetFirst();

    for (int i = 0; ; )
    {
        if (pCluster == NULL)
        {
            pBlockEntry = GetEOS();
            return 1;
        }

        if (pCluster->EOS())
        {
            if (m_pSegment->Unparsed() <= 0)  //all clusters have been loaded
            {
                pBlockEntry = GetEOS();
                return 1;
            }

            pBlockEntry = 0;
            return E_BUFFER_NOT_FULL;
        }

        pBlockEntry = pCluster->GetFirst();

        if (pBlockEntry == 0)  //empty cluster
        {
            pCluster = m_pSegment->GetNext(pCluster);
            continue;
        }

        for (;;)
        {
            const Block* const pBlock = pBlockEntry->GetBlock();
            assert(pBlock);

            const long long tn = pBlock->GetTrackNumber();

            if ((tn == m_info.number) && VetEntry(pBlockEntry))
                return 0;

            pBlockEntry = pCluster->GetNext(pBlockEntry);

            if (pBlockEntry == 0)
                break;
        }

        ++i;

        if (i >= 100)
            break;

        pCluster = m_pSegment->GetNext(pCluster);
    }

    //NOTE: if we get here, it means that we didn't find a block with
    //a matching track number.  We interpret that as an error (which
    //might be too conservative).

    pBlockEntry = GetEOS();  //so we can return a non-NULL value
    return 1;
}


long Track::GetNext(
    const BlockEntry* pCurrEntry,
    const BlockEntry*& pNextEntry) const
{
    assert(pCurrEntry);
    assert(!pCurrEntry->EOS());  //?

    const Block* const pCurrBlock = pCurrEntry->GetBlock();
    assert(pCurrBlock->GetTrackNumber() == m_info.number);

    const Cluster* pCluster = pCurrEntry->GetCluster();
    assert(pCluster);
    assert(!pCluster->EOS());

    pNextEntry = pCluster->GetNext(pCurrEntry);

    for (int i = 0; ; )
    {
        while (pNextEntry)
        {
            const Block* const pNextBlock = pNextEntry->GetBlock();
            assert(pNextBlock);

            if (pNextBlock->GetTrackNumber() == m_info.number)
                return 0;

            pNextEntry = pCluster->GetNext(pNextEntry);
        }

        pCluster = m_pSegment->GetNext(pCluster);

        if (pCluster == NULL)
        {
            pNextEntry = GetEOS();
            return 1;
        }

        if (pCluster->EOS())
        {
            if (m_pSegment->Unparsed() <= 0)   //all clusters have been loaded
            {
                pNextEntry = GetEOS();
                return 1;
            }

            //TODO: there is a potential O(n^2) problem here: we tell the
            //caller to (pre)load another cluster, which he does, but then he
            //calls GetNext again, which repeats the same search.  This is
            //a pathological case, since the only way it can happen is if
            //there exists a long sequence of clusters none of which contain a
            // block from this track.  One way around this problem is for the
            //caller to be smarter when he loads another cluster: don't call
            //us back until you have a cluster that contains a block from this
            //track. (Of course, that's not cheap either, since our caller
            //would have to scan the each cluster as it's loaded, so that
            //would just push back the problem.)

            pNextEntry = NULL;
            return E_BUFFER_NOT_FULL;
        }

        pNextEntry = pCluster->GetFirst();

        if (pNextEntry == NULL)  //empty cluster
            continue;

        ++i;

        if (i >= 100)
            break;
    }

    //NOTE: if we get here, it means that we didn't find a block with
    //a matching track number after lots of searching, so we give
    //up trying.

    pNextEntry = GetEOS();  //so we can return a non-NULL value
    return 1;
}


Track::EOSBlock::EOSBlock()
{
}


bool Track::EOSBlock::EOS() const
{
    return true;
}


const Cluster* Track::EOSBlock::GetCluster() const
{
    return NULL;
}


size_t Track::EOSBlock::GetIndex() const
{
    return 0;
}


const Block* Track::EOSBlock::GetBlock() const
{
    return NULL;
}


bool Track::EOSBlock::IsBFrame() const
{
    return false;
}


VideoTrack::VideoTrack(
    Segment* pSegment,
    const Info& i,
    long long element_start,
    long long element_size) :
    Track(pSegment, i, element_start, element_size),
    m_width(-1),
    m_height(-1),
    m_rate(-1)
{
    assert(i.type == 1);
    assert(i.number > 0);

    IMkvReader* const pReader = pSegment->m_pReader;

    const Settings& s = i.settings;
    assert(s.start >= 0);
    assert(s.size >= 0);

    long long pos = s.start;
    assert(pos >= 0);

    const long long stop = pos + s.size;

    while (pos < stop)
    {
#ifdef _DEBUG
        long len;
        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO: handle error case
        assert((pos + len) <= stop);
#endif
        if (Match(pReader, pos, 0x30, m_width))
            ;
        else if (Match(pReader, pos, 0x3A, m_height))
            ;
        else if (Match(pReader, pos, 0x0383E3, m_rate))
            ;
        else
        {
            long len;
            const long long id = ReadUInt(pReader, pos, len);
            assert(id >= 0);  //TODO: handle error case
            assert((pos + len) <= stop);

            pos += len;  //consume id

            const long long size = ReadUInt(pReader, pos, len);
            assert(size >= 0);  //TODO: handle error case
            assert((pos + len) <= stop);

            pos += len;  //consume length of size
            assert((pos + size) <= stop);

            //pos now designates start of payload

            pos += size;  //consume payload
            assert(pos <= stop);
        }
    }

    return;
}


bool VideoTrack::VetEntry(const BlockEntry* pBlockEntry) const
{
    assert(pBlockEntry);

    const Block* const pBlock = pBlockEntry->GetBlock();
    assert(pBlock);
    assert(pBlock->GetTrackNumber() == m_info.number);

    return pBlock->IsKey();
}


long VideoTrack::Seek(
    long long time_ns,
    const BlockEntry*& pResult) const
{
    const long status = GetFirst(pResult);

    if (status < 0)  //buffer underflow, etc
        return status;

    assert(pResult);

    if (pResult->EOS())
        return 0;

    const Cluster* pCluster = pResult->GetCluster();
    assert(pCluster);
    assert(pCluster->GetIndex() >= 0);

    if (time_ns <= pResult->GetBlock()->GetTime(pCluster))
        return 0;

    Cluster** const clusters = m_pSegment->m_clusters;
    assert(clusters);

    const long count = m_pSegment->GetCount();  //loaded only, not pre-loaded
    assert(count > 0);

    Cluster** const i = clusters + pCluster->GetIndex();
    assert(i);
    assert(*i == pCluster);
    assert(pCluster->GetTime() <= time_ns);

    Cluster** const j = clusters + count;

    Cluster** lo = i;
    Cluster** hi = j;

    while (lo < hi)
    {
        //INVARIANT:
        //[i, lo) <= time_ns
        //[lo, hi) ?
        //[hi, j)  > time_ns

        Cluster** const mid = lo + (hi - lo) / 2;
        assert(mid < hi);

        pCluster = *mid;
        assert(pCluster);
        assert(pCluster->GetIndex() >= 0);
        assert(pCluster->GetIndex() == long(mid - m_pSegment->m_clusters));

        const long long t = pCluster->GetTime();

        if (t <= time_ns)
            lo = mid + 1;
        else
            hi = mid;

        assert(lo <= hi);
    }

    assert(lo == hi);
    assert(lo > i);
    assert(lo <= j);

    pCluster = *--lo;
    assert(pCluster);
    assert(pCluster->GetTime() <= time_ns);

    pResult = pCluster->GetEntry(this, time_ns);

    if ((pResult != 0) && !pResult->EOS())  //found a keyframe
        return 0;

    while (lo != i)
    {
        pCluster = *--lo;
        assert(pCluster);
        assert(pCluster->GetTime() <= time_ns);

        //TODO:
        //We need to handle the case when a cluster
        //contains multiple keyframes.  Simply returning
        //the largest keyframe on the cluster isn't
        //good enough.
        pResult = pCluster->GetMaxKey(this);

        if ((pResult != 0) && !pResult->EOS())
            return 0;
    }

    //weird: we're on the first cluster, but no keyframe found
    //should never happen but we must return something anyway

    pResult = GetEOS();
    return 0;
}


long long VideoTrack::GetWidth() const
{
    return m_width;
}


long long VideoTrack::GetHeight() const
{
    return m_height;
}


double VideoTrack::GetFrameRate() const
{
    return m_rate;
}


AudioTrack::AudioTrack(
    Segment* pSegment,
    const Info& i,
    long long element_start,
    long long element_size) :
    Track(pSegment, i, element_start, element_size),
    m_rate(0.0),
    m_channels(0),
    m_bitDepth(-1)
{
    assert(i.type == 2);
    assert(i.number > 0);

    IMkvReader* const pReader = pSegment->m_pReader;

    const Settings& s = i.settings;
    assert(s.start >= 0);
    assert(s.size >= 0);

    long long pos = s.start;
    assert(pos >= 0);

    const long long stop = pos + s.size;

    while (pos < stop)
    {
#ifdef _DEBUG
        long len;
        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO: handle error case
        assert((pos + len) <= stop);
#endif
        if (Match(pReader, pos, 0x35, m_rate))
            ;
        else if (Match(pReader, pos, 0x1F, m_channels))
            ;
        else if (Match(pReader, pos, 0x2264, m_bitDepth))
            ;
        else
        {
            long len;
            const long long id = ReadUInt(pReader, pos, len);
            assert(id >= 0);  //TODO: handle error case
            assert((pos + len) <= stop);

            pos += len;  //consume id

            const long long size = ReadUInt(pReader, pos, len);
            assert(size >= 0);  //TODO: handle error case
            assert((pos + len) <= stop);

            pos += len;  //consume length of size
            assert((pos + size) <= stop);

            //pos now designates start of payload

            pos += size;  //consume payload
            assert(pos <= stop);
        }
    }

    if (m_channels <= 0)
        m_channels = 1;  //Matroska spec says this is the default

    return;
}


bool AudioTrack::VetEntry(const BlockEntry* pBlockEntry) const
{
    assert(pBlockEntry);

    const Block* const pBlock = pBlockEntry->GetBlock();
    assert(pBlock);
    assert(pBlock->GetTrackNumber() == m_info.number);

    return true;
}


long AudioTrack::Seek(
    long long time_ns,
    const BlockEntry*& pResult) const
{
    const long status = GetFirst(pResult);

    if (status < 0)  //buffer underflow, etc
        return status;

    assert(pResult);

    if (pResult->EOS())
        return 0;

    const Cluster* pCluster = pResult->GetCluster();
    assert(pCluster);
    assert(pCluster->GetIndex() >= 0);

    if (time_ns <= pResult->GetBlock()->GetTime(pCluster))
        return 0;

    Cluster** const clusters = m_pSegment->m_clusters;
    assert(clusters);

    const long count = m_pSegment->GetCount();  //loaded only, not preloaded
    assert(count > 0);

    Cluster** const i = clusters + pCluster->GetIndex();
    assert(i);
    assert(*i == pCluster);
    assert(pCluster->GetTime() <= time_ns);

    Cluster** const j = clusters + count;

    Cluster** lo = i;
    Cluster** hi = j;

    while (lo < hi)
    {
        //INVARIANT:
        //[i, lo) <= time_ns
        //[lo, hi) ?
        //[hi, j)  > time_ns

        Cluster** const mid = lo + (hi - lo) / 2;
        assert(mid < hi);

        pCluster = *mid;
        assert(pCluster);
        assert(pCluster->GetIndex() >= 0);
        assert(pCluster->GetIndex() == long(mid - m_pSegment->m_clusters));

        const long long t = pCluster->GetTime();

        if (t <= time_ns)
            lo = mid + 1;
        else
            hi = mid;

        assert(lo <= hi);
    }

    assert(lo == hi);
    assert(lo > i);
    assert(lo <= j);

    while (lo > i)
    {
        pCluster = *--lo;
        assert(pCluster);
        assert(pCluster->GetTime() <= time_ns);

        pResult = pCluster->GetEntry(this);

        if ((pResult != 0) && !pResult->EOS())
            return 0;

        //landed on empty cluster (no entries)
    }

    pResult = GetEOS();  //weird
    return 0;
}


double AudioTrack::GetSamplingRate() const
{
    return m_rate;
}


long long AudioTrack::GetChannels() const
{
    return m_channels;
}

long long AudioTrack::GetBitDepth() const
{
    return m_bitDepth;
}

Tracks::Tracks(
    Segment* pSegment,
    long long start,
    long long size_,
    long long element_start,
    long long element_size) :
    m_pSegment(pSegment),
    m_start(start),
    m_size(size_),
    m_trackEntries(NULL),
    m_trackEntriesEnd(NULL),
    m_element_start(element_start),
    m_element_size(element_size)
{
    long long stop = m_start + m_size;
    IMkvReader* const pReader = m_pSegment->m_pReader;

    long long pos1 = m_start;
    int count = 0;

    while (pos1 < stop)
    {
        long len;
        const long long id = ReadUInt(pReader, pos1, len);
        assert(id >= 0);
        assert((pos1 + len) <= stop);

        pos1 += len;  //consume id

        const long long size = ReadUInt(pReader, pos1, len);
        assert(size >= 0);
        assert((pos1 + len) <= stop);

        pos1 += len;  //consume length of size

        //pos now desinates start of element
        if (id == 0x2E)  //TrackEntry ID
            ++count;

        pos1 += size;  //consume payload
        assert(pos1 <= stop);
    }

    if (count <= 0)
        return;

    m_trackEntries = new Track*[count];
    m_trackEntriesEnd = m_trackEntries;

    long long pos = m_start;

    while (pos < stop)
    {
        long len;
        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);
        assert((pos + len) <= stop);

        const long long element_start = pos;

        pos += len;  //consume id

        const long long size1 = ReadUInt(pReader, pos, len);
        assert(size1 >= 0);
        assert((pos + len) <= stop);

        pos += len;  //consume length of size

        //pos now desinates start of element

        const long long element_size = size1 + pos - element_start;

        if (id == 0x2E)  //TrackEntry ID
        {
            Track*& pTrack = *m_trackEntriesEnd;
            ParseTrackEntry(pos, size1, pTrack, element_start, element_size);

            if (pTrack)
                ++m_trackEntriesEnd;
        }

        pos += size1;  //consume payload
        assert(pos <= stop);
    }
}


unsigned long Tracks::GetTracksCount() const
{
    const ptrdiff_t result = m_trackEntriesEnd - m_trackEntries;
    assert(result >= 0);

    return static_cast<unsigned long>(result);
}


void Tracks::ParseTrackEntry(
    long long start,
    long long size,
    Track*& pTrack,
    long long element_start,
    long long element_size)
{
    IMkvReader* const pReader = m_pSegment->m_pReader;

    long long pos = start;
    const long long stop = start + size;

    Track::Info i;

    Track::Settings videoSettings;
    videoSettings.start = -1;

    Track::Settings audioSettings;
    audioSettings.start = -1;

    long long lacing = 1;  //default is true

    while (pos < stop)
    {
#ifdef _DEBUG
        long len;
        const long long id = ReadUInt(pReader, pos, len);
        len;
        id;
#endif
        if (Match(pReader, pos, 0x57, i.number))
            assert(i.number > 0);
        //else if (Match(pReader, pos, 0x33C5, i.uid))
        //    ;
        else if (Match(pReader, pos, 0x03, i.type))
            ;
        else if (Match(pReader, pos, 0x136E, i.nameAsUTF8))
            assert(i.nameAsUTF8);
        else if (Match(pReader, pos, 0x06, i.codecId))
            ;
        else if (Match(pReader, pos, 0x1C, lacing))
            assert(lacing <= 1);
        else if (Match(pReader,
                       pos,
                       0x23A2,
                       i.codecPrivate,
                       i.codecPrivateSize))
            ;
        else if (Match(pReader, pos, 0x058688, i.codecNameAsUTF8))
            assert(i.codecNameAsUTF8);
        else
        {
            long len;

            const long long idpos = pos;
            idpos;

            const long long id = ReadUInt(pReader, pos, len);
            assert(id >= 0);  //TODO: handle error case
            assert((pos + len) <= stop);

            pos += len;  //consume id

            const long long size = ReadUInt(pReader, pos, len);
            assert(size >= 0);  //TODO: handle error case
            assert((pos + len) <= stop);

            pos += len;  //consume length of size
            const long long start = pos;

            pos += size;  //consume payload
            assert(pos <= stop);

            if (id == 0x60)
            {
                videoSettings.start = start;
                videoSettings.size = size;
            }
            else if (id == 0x61)
            {
                audioSettings.start = start;
                audioSettings.size = size;
            }
            else if (id == 0x33C5)  //Track UID
            {
                assert(size <= 8);

                i.uid = 0;
                long long pos_ = start;
                const long long pos_end = start + size;

                while (pos_ != pos_end)
                {
                    unsigned char b;

                    const long status = pReader->Read(pos_, 1, &b);
                    assert(status == 0);

                    i.uid <<= 8;
                    i.uid |= b;

                    ++pos_;
                }
            }
        }
    }

    assert(pos == stop);
    //TODO: propertly vet info.number, to ensure both its existence,
    //and that it is unique among all tracks.
    assert(i.number > 0);

    i.lacing = (lacing > 0) ? true : false;

    //TODO: vet settings, to ensure that video settings (0x60)
    //were specified when type = 1, and that audio settings (0x61)
    //were specified when type = 2.
    if (i.type == 1)  //video
    {
        assert(audioSettings.start < 0);
        assert(videoSettings.start >= 0);

        i.settings = videoSettings;

        VideoTrack* const t = new VideoTrack(
            m_pSegment,
            i,
            element_start,
            element_size);
        assert(t);  //TODO
        pTrack = t;
    }
    else if (i.type == 2)  //audio
    {
        assert(videoSettings.start < 0);
        assert(audioSettings.start >= 0);

        i.settings = audioSettings;

        AudioTrack* const t = new  AudioTrack(
            m_pSegment,
            i,
            element_start,
            element_size);
        assert(t);  //TODO
        pTrack = t;
    }
    else
    {
        // for now we do not support other track types yet.
        // TODO: support other track types
        i.Clear();

        pTrack = NULL;
    }

    return;
}


Tracks::~Tracks()
{
    Track** i = m_trackEntries;
    Track** const j = m_trackEntriesEnd;

    while (i != j)
    {
        Track* const pTrack = *i++;
        delete pTrack;
    }

    delete[] m_trackEntries;
}

const Track* Tracks::GetTrackByNumber(unsigned long tn_) const
{
    const long long tn = tn_;

    Track** i = m_trackEntries;
    Track** const j = m_trackEntriesEnd;

    while (i != j)
    {
        Track* const pTrack = *i++;

        if (pTrack == NULL)
            continue;

        if (tn == pTrack->GetNumber())
            return pTrack;
    }

    return NULL;  //not found
}


const Track* Tracks::GetTrackByIndex(unsigned long idx) const
{
    const ptrdiff_t count = m_trackEntriesEnd - m_trackEntries;

    if (idx >= static_cast<unsigned long>(count))
         return NULL;

    return m_trackEntries[idx];
}

#if 0
long long Cluster::Unparsed() const
{
    if (m_timecode < 0)  //not even partially loaded
        return LLONG_MAX;

    assert(m_pos >= m_element_start);
    //assert(m_element_size > m_size);

    const long long element_stop = m_element_start + m_element_size;
    assert(m_pos <= element_stop);

    const long long result = element_stop - m_pos;
    assert(result >= 0);

    return result;
}
#endif


#if 0
void Cluster::Load() const
{
    assert(m_pSegment);
    assert(m_pos >= m_element_start);
    //assert(m_size);

    if (m_timecode >= 0)  //loaded
        return;

    assert(m_pos == m_element_start);

    IMkvReader* const pReader = m_pSegment->m_pReader;

    long len;

    const long long id_ = ReadUInt(pReader, m_pos, len);
    assert(id_ >= 0);
    assert(id_ == 0x0F43B675);  //Cluster ID

    m_pos += len;  //consume id

    const long long cluster_size = ReadUInt(pReader, m_pos, len);
    assert(cluster_size >= 0);  //TODO

    const long long unknown_size = (1LL << (7 * len)) - 1;
    unknown_size;
    assert(cluster_size != unknown_size);  //TODO

    m_pos += len;  //consume size field

    const long long stop = m_pos + cluster_size;

    const long long element_size = stop - m_element_start;
    assert((m_element_size <= 0) || (m_element_size == element_size));

    if (m_element_size <= 0)
        m_element_size = element_size;

    long long timecode = -1;

    while (m_pos < stop)
    {
        if (Match(pReader, m_pos, 0x67, timecode))
            break;
        else
        {
            const long long id = ReadUInt(pReader, m_pos, len);
            assert(id >= 0);  //TODO
            assert((m_pos + len) <= stop);

            m_pos += len;  //consume id

            const long long size = ReadUInt(pReader, m_pos, len);
            assert(size >= 0);  //TODO
            assert((m_pos + len) <= stop);

            m_pos += len;  //consume size

            if (id == 0x20)  //BlockGroup ID
                break;

            if (id == 0x23)  //SimpleBlock ID
                break;

            m_pos += size;  //consume payload
            assert(m_pos <= stop);
        }
    }

    assert(m_pos <= stop);
    assert(timecode >= 0);

    m_timecode = timecode;
}
#endif


long Cluster::Load(long long& pos, long& len) const
{
    assert(m_pSegment);
    assert(m_pos >= m_element_start);

    if (m_timecode >= 0)  //at least partially loaded
        return 0;

    assert(m_pos == m_element_start);
    assert(m_element_size < 0);

    IMkvReader* const pReader = m_pSegment->m_pReader;

    long long total, avail;

    const int status = pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));
    assert((total < 0) || (m_pos <= total));  //TODO: verify this

    pos = m_pos;

    long long cluster_size = -1;

    {
        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error or underflow
            return static_cast<long>(result);

        if (result > 0)  //underflow (weird)
            return E_BUFFER_NOT_FULL;

        //if ((pos + len) > segment_stop)
        //    return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long id_ = ReadUInt(pReader, pos, len);

        if (id_ < 0)  //error
            return static_cast<long>(id_);

        if (id_ != 0x0F43B675)  //Cluster ID
            return E_FILE_FORMAT_INVALID;

        pos += len;  //consume id

        //read cluster size

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        //if ((pos + len) > segment_stop)
        //    return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(cluster_size);

        if (size == 0)
            return E_FILE_FORMAT_INVALID;  //TODO: verify this

        pos += len;  //consume length of size of element

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size != unknown_size)
            cluster_size = size;
    }

    //pos points to start of payload

#if 0
    len = static_cast<long>(size_);

    if (cluster_stop > avail)
        return E_BUFFER_NOT_FULL;
#endif

    long long timecode = -1;
    long long new_pos = -1;
    bool bBlock = false;

    long long cluster_stop = (cluster_size < 0) ? -1 : pos + cluster_size;

    for (;;)
    {
        if ((cluster_stop >= 0) && (pos >= cluster_stop))
            break;

        //Parse ID

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long id = ReadUInt(pReader, pos, len);

        if (id < 0) //error
            return static_cast<long>(id);

        if (id == 0)
            return E_FILE_FORMAT_INVALID;

        //This is the distinguished set of ID's we use to determine
        //that we have exhausted the sub-element's inside the cluster
        //whose ID we parsed earlier.

        if (id == 0x0F43B675)  //Cluster ID
            break;

        if (id == 0x0C53BB6B)  //Cues ID
            break;

        pos += len;  //consume ID field

        //Parse Size

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size == unknown_size)
            return E_FILE_FORMAT_INVALID;

        pos += len;  //consume size field

        if ((cluster_stop >= 0) && (pos > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        //pos now points to start of payload

        if (size == 0)  //weird
            continue;

        if ((cluster_stop >= 0) && ((pos + size) > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if (id == 0x67)  //TimeCode ID
        {
            len = static_cast<long>(size);

            if ((pos + size) > avail)
                return E_BUFFER_NOT_FULL;

            timecode = UnserializeUInt(pReader, pos, size);

            if (timecode < 0)  //error (or underflow)
                return static_cast<long>(timecode);

            new_pos = pos + size;

            if (bBlock)
                break;
        }
        else if (id == 0x20)  //BlockGroup ID
        {
            bBlock = true;
            break;
        }
        else if (id == 0x23)  //SimpleBlock ID
        {
            bBlock = true;
            break;
        }

        pos += size;  //consume payload
        assert((cluster_stop < 0) || (pos <= cluster_stop));
    }

    assert((cluster_stop < 0) || (pos <= cluster_stop));

    if (timecode < 0)  //no timecode found
        return E_FILE_FORMAT_INVALID;

    if (!bBlock)
        return E_FILE_FORMAT_INVALID;

    m_pos = new_pos;  //designates position just beyond timecode payload
    m_timecode = timecode;  // m_timecode >= 0 means we're partially loaded

    if (cluster_size >= 0)
        m_element_size = cluster_stop - m_element_start;

    return 0;
}


long Cluster::Parse(long long& pos, long& len) const
{
    long status = Load(pos, len);

    if (status < 0)
        return status;

    assert(m_pos >= m_element_start);
    assert(m_timecode >= 0);
    //assert(m_size > 0);
    //assert(m_element_size > m_size);

    const long long cluster_stop =
        (m_element_size < 0) ? -1 : m_element_start + m_element_size;

    if ((cluster_stop >= 0) && (m_pos >= cluster_stop))
        return 1;  //nothing else to do

    IMkvReader* const pReader = m_pSegment->m_pReader;

    long long total, avail;

    status = pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    pos = m_pos;

    for (;;)
    {
        if ((cluster_stop >= 0) && (pos >= cluster_stop))
            break;

        if ((total >= 0) && (pos >= total))
        {
            if (m_element_size < 0)
                m_element_size = pos - m_element_start;

            break;
        }

        //Parse ID

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long id = ReadUInt(pReader, pos, len);

        if (id < 0) //error
            return static_cast<long>(id);

        if (id == 0)  //weird
            return E_FILE_FORMAT_INVALID;

        //This is the distinguished set of ID's we use to determine
        //that we have exhausted the sub-element's inside the cluster
        //whose ID we parsed earlier.

        if ((id == 0x0F43B675) || (id == 0x0C53BB6B)) //Cluster or Cues ID
        {
            if (m_element_size < 0)
                m_element_size = pos - m_element_start;

            break;
        }

        pos += len;  //consume ID field

        //Parse Size

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size == unknown_size)
            return E_FILE_FORMAT_INVALID;

        pos += len;  //consume size field

        if ((cluster_stop >= 0) && (pos > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        //pos now points to start of payload

        if (size == 0)  //weird
            continue;

        //const long long block_start = pos;
        const long long block_stop = pos + size;

        if (cluster_stop >= 0)
        {
            if (block_stop > cluster_stop)
                return E_FILE_FORMAT_INVALID;
        }
        else if ((total >= 0) && (block_stop > total))
        {
            m_element_size = total - m_element_start;
            pos = total;
            break;
        }
        else if (block_stop > avail)
        {
            len = static_cast<long>(size);
            return E_BUFFER_NOT_FULL;
        }

        if (id == 0x20)  //BlockGroup
            return ParseBlockGroup(size, pos, len);

        if (id == 0x23)  //SimpleBlock
            return ParseSimpleBlock(size, pos, len);

        pos += size;  //consume payload
        assert((cluster_stop < 0) || (pos <= cluster_stop));
    }

    assert(m_element_size > 0);

    m_pos = pos;
    assert((cluster_stop < 0) || (m_pos <= cluster_stop));

    if (m_entries_count > 0)
    {
        const long idx = m_entries_count - 1;

        const BlockEntry* const pLast = m_entries[idx];
        assert(pLast);

        const Block* const pBlock = pLast->GetBlock();
        assert(pBlock);

        const long long start = pBlock->m_start;

        if ((total >= 0) && (start > total))
            return -1;  //defend against trucated stream

        const long long size = pBlock->m_size;

        const long long stop = start + size;
        assert((cluster_stop < 0) || (stop <= cluster_stop));

        if ((total >= 0) && (stop > total))
            return -1;  //defend against trucated stream
    }

    return 1;  //no more entries
}


long Cluster::ParseSimpleBlock(
    long long block_size,
    long long& pos,
    long& len) const
{
    const long long block_start = pos;
    const long long block_stop = pos + block_size;

    IMkvReader* const pReader = m_pSegment->m_pReader;

    long long total, avail;

    long status = pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    //parse track number

    if ((pos + 1) > avail)
    {
        len = 1;
        return E_BUFFER_NOT_FULL;
    }

    long long result = GetUIntLength(pReader, pos, len);

    if (result < 0)  //error
        return static_cast<long>(result);

    if (result > 0)  //weird
        return E_BUFFER_NOT_FULL;

    if ((pos + len) > block_stop)
        return E_FILE_FORMAT_INVALID;

    if ((pos + len) > avail)
        return E_BUFFER_NOT_FULL;

    const long long track = ReadUInt(pReader, pos, len);

    if (track < 0) //error
        return static_cast<long>(track);

    if (track == 0)
        return E_FILE_FORMAT_INVALID;

    const Tracks* const pTracks = m_pSegment->GetTracks();
    assert(pTracks);

    const long tn = static_cast<long>(track);

    const Track* const pTrack = pTracks->GetTrackByNumber(tn);

    if (pTrack == NULL)
        return E_FILE_FORMAT_INVALID;

    pos += len;  //consume track number

    if ((pos + 2) > block_stop)
        return E_FILE_FORMAT_INVALID;

    if ((pos + 2) > avail)
    {
        len = 2;
        return E_BUFFER_NOT_FULL;
    }

    pos += 2;  //consume timecode

    if ((pos + 1) > block_stop)
        return E_FILE_FORMAT_INVALID;

    if ((pos + 1) > avail)
    {
        len = 1;
        return E_BUFFER_NOT_FULL;
    }

    unsigned char flags;

    status = pReader->Read(pos, 1, &flags);

    if (status < 0)  //error or underflow
    {
        len = 1;
        return status;
    }

    ++pos;  //consume flags byte
    assert(pos <= avail);

    if (pos >= block_stop)
        return E_FILE_FORMAT_INVALID;

    const int lacing = int(flags & 0x06) >> 1;

    if ((lacing != 0) && (block_stop > avail))
    {
        len = static_cast<long>(block_stop - pos);
        return E_BUFFER_NOT_FULL;
    }

    CreateBlock(0x23, block_start, block_size);  //simple block id
    m_pos = block_stop;

    return 0;  //success
}


long Cluster::ParseBlockGroup(
    long long payload_size,
    long long& pos,
    long& len) const
{
    const long long payload_start = pos;
    const long long payload_stop = pos + payload_size;

    IMkvReader* const pReader = m_pSegment->m_pReader;

    long long total, avail;

    long status = pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    if ((total >= 0) && (payload_stop > total))
        return E_FILE_FORMAT_INVALID;

    if (payload_stop > avail)
    {
         len = static_cast<long>(payload_size);
         return E_BUFFER_NOT_FULL;
    }

    while (pos < payload_stop)
    {
        //parse sub-block element ID

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((pos + len) > payload_stop)
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long id = ReadUInt(pReader, pos, len);

        if (id < 0) //error
            return static_cast<long>(id);

        if (id == 0)  //not a value ID
            return E_FILE_FORMAT_INVALID;

        pos += len;  //consume ID field

        //Parse Size

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((pos + len) > payload_stop)
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        pos += len;  //consume size field

        //pos now points to start of sub-block group payload

        if (pos > payload_stop)
            return E_FILE_FORMAT_INVALID;

        if (size == 0)  //weird
            continue;

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size == unknown_size)
            return E_FILE_FORMAT_INVALID;

        if (id != 0x21)  //sub-part of BlockGroup is not a Block
        {
            pos += size;  //consume sub-part of block group

            if (pos > payload_stop)
                return E_FILE_FORMAT_INVALID;

            continue;
        }

        const long long block_stop = pos + size;

        if (block_stop > payload_stop)
            return E_FILE_FORMAT_INVALID;

        //parse track number

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((pos + len) > block_stop)
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long track = ReadUInt(pReader, pos, len);

        if (track < 0) //error
            return static_cast<long>(track);

        if (track == 0)
            return E_FILE_FORMAT_INVALID;

        const Tracks* const pTracks = m_pSegment->GetTracks();
        assert(pTracks);

        const long tn = static_cast<long>(track);

        const Track* const pTrack = pTracks->GetTrackByNumber(tn);

        if (pTrack == NULL)
            return E_FILE_FORMAT_INVALID;

        pos += len;  //consume track number

        if ((pos + 2) > block_stop)
            return E_FILE_FORMAT_INVALID;

        if ((pos + 2) > avail)
        {
            len = 2;
            return E_BUFFER_NOT_FULL;
        }

        pos += 2;  //consume timecode

        if ((pos + 1) > block_stop)
            return E_FILE_FORMAT_INVALID;

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        unsigned char flags;

        status = pReader->Read(pos, 1, &flags);

        if (status < 0)  //error or underflow
        {
            len = 1;
            return status;
        }

        ++pos;  //consume flags byte
        assert(pos <= avail);

        if (pos >= block_stop)
            return E_FILE_FORMAT_INVALID;

        const int lacing = int(flags & 0x06) >> 1;

        if ((lacing != 0) && (block_stop > avail))
        {
            len = static_cast<long>(block_stop - pos);
            return E_BUFFER_NOT_FULL;
        }

        pos = block_stop;  //consume block-part of block group
        assert(pos <= payload_stop);
    }

    assert(pos == payload_stop);

    CreateBlock(0x20, payload_start, payload_size);  //BlockGroup ID
    m_pos = payload_stop;

    return 0;  //success
}


long Cluster::GetEntry(long index, const mkvparser::BlockEntry*& pEntry) const
{
    assert(m_pos >= m_element_start);

    pEntry = 0;

    if (index < 0)
        return -1;  //generic error

    if (m_entries_count < 0)
        return E_BUFFER_NOT_FULL;

    assert(m_entries);
    assert(m_entries_size > 0);
    assert(m_entries_count <= m_entries_size);

    if (index < m_entries_count)
    {
        pEntry = m_entries[index];
        assert(pEntry);

        return 1;  //found entry
    }

    if (m_element_size < 0)        //we don't know cluster end yet
        return E_BUFFER_NOT_FULL;  //underflow

    const long long element_stop = m_element_start + m_element_size;

    if (m_pos >= element_stop)
        return 0;  //nothing left to parse

    return E_BUFFER_NOT_FULL;  //underflow, since more remains to be parsed
}


Cluster* Cluster::Create(
    Segment* pSegment,
    long idx,
    long long off)
    //long long element_size)
{
    assert(pSegment);
    assert(off >= 0);

    const long long element_start = pSegment->m_start + off;

    Cluster* const pCluster = new Cluster(pSegment,
                                          idx,
                                          element_start);
                                          //element_size);
    assert(pCluster);

    return pCluster;
}


Cluster::Cluster() :
    m_pSegment(NULL),
    m_index(0),
    m_pos(0),
    //m_size(0),
    m_element_start(0),
    m_element_size(0),
    m_timecode(0),
    m_entries(NULL),
    m_entries_size(0),
    m_entries_count(0)  //means "no entries"
{
}


Cluster::Cluster(
    Segment* pSegment,
    long idx,
    long long element_start
    /* long long element_size */ ) :
    m_pSegment(pSegment),
    m_index(idx),
    m_pos(element_start),
    m_element_start(element_start),
    m_element_size(-1 /* element_size */ ),
    //m_size(-1),
    m_timecode(-1),
    m_entries(NULL),
    m_entries_size(0),
    m_entries_count(-1)  //means "has not been parsed yet"
{
}


Cluster::~Cluster()
{
    if (m_entries_count <= 0)
        return;

    BlockEntry** i = m_entries;
    BlockEntry** const j = m_entries + m_entries_count;

    while (i != j)
    {
         BlockEntry* p = *i++;
         assert(p);

         delete p;
    }

    delete[] m_entries;
}


bool Cluster::EOS() const
{
    return (m_pSegment == NULL);
}


long Cluster::GetIndex() const
{
    return m_index;
}


long long Cluster::GetPosition() const
{
    const long long pos = m_element_start - m_pSegment->m_start;
    assert(pos >= 0);

    return pos;
}


long long Cluster::GetElementSize() const
{
    return m_element_size;
}


#if 0
bool Cluster::HasBlockEntries(
    const Segment* pSegment,
    long long off)  //relative to start of segment payload
{
    assert(pSegment);
    assert(off >= 0);  //relative to segment

    IMkvReader* const pReader = pSegment->m_pReader;

    long long pos = pSegment->m_start + off;  //absolute
    long long size;

    {
        long len;

        const long long id = ReadUInt(pReader, pos, len);
        id;
        assert(id >= 0);
        assert(id == 0x0F43B675);  //Cluster ID

        pos += len;  //consume id

        size = ReadUInt(pReader, pos, len);
        assert(size > 0);

        pos += len;  //consume size

        //pos now points to start of payload
    }

    const long long stop = pos + size;

    while (pos < stop)
    {
        long len;

        const long long id = ReadUInt(pReader, pos, len);
        assert(id >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume id

        const long long size = ReadUInt(pReader, pos, len);
        assert(size >= 0);  //TODO
        assert((pos + len) <= stop);

        pos += len;  //consume size

        if (id == 0x20)  //BlockGroup ID
            return true;

        if (id == 0x23)  //SimpleBlock ID
            return true;

        pos += size;  //consume payload
        assert(pos <= stop);
    }

    return false;
}
#endif


long Cluster::HasBlockEntries(
    const Segment* pSegment,
    long long off,  //relative to start of segment payload
    long long& pos,
    long& len)
{
    assert(pSegment);
    assert(off >= 0);  //relative to segment

    IMkvReader* const pReader = pSegment->m_pReader;

    long long total, avail;

    long status = pReader->Length(&total, &avail);

    if (status < 0)  //error
        return status;

    assert((total < 0) || (avail <= total));

    pos = pSegment->m_start + off;  //absolute

    if ((total >= 0) && (pos >= total))
        return 0;  //we don't even have a complete cluster

    const long long segment_stop =
        (pSegment->m_size < 0) ? -1 : pSegment->m_start + pSegment->m_size;

    long long cluster_stop = -1;  //interpreted later to mean "unknown size"

    {
        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //need more data
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((total >= 0) && ((pos + len) > total))
            return 0;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long id = ReadUInt(pReader, pos, len);

        if (id < 0)  //error
            return static_cast<long>(id);

        if (id != 0x0F43B675)  //weird: not cluster ID
            return -1;         //generic error

        pos += len;  //consume Cluster ID field

        //read size field

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //weird
            return E_BUFFER_NOT_FULL;

        if ((segment_stop >= 0) && ((pos + len) > segment_stop))
            return E_FILE_FORMAT_INVALID;

        if ((total >= 0) && ((pos + len) > total))
            return 0;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        if (size == 0)
            return 0;  //cluster does not have entries

        pos += len;  //consume size field

        //pos now points to start of payload

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size != unknown_size)
        {
            cluster_stop = pos + size;
            assert(cluster_stop >= 0);

            if ((segment_stop >= 0) && (cluster_stop > segment_stop))
                return E_FILE_FORMAT_INVALID;

            if ((total >= 0) && (cluster_stop > total))
                //return E_FILE_FORMAT_INVALID;  //too conservative
                return 0;  //cluster does not have any entries
        }
    }

    for (;;)
    {
        if ((cluster_stop >= 0) && (pos >= cluster_stop))
            return 0;  //no entries detected

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        long long result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //need more data
            return E_BUFFER_NOT_FULL;

        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long id = ReadUInt(pReader, pos, len);

        if (id < 0)  //error
            return static_cast<long>(id);

        //This is the distinguished set of ID's we use to determine
        //that we have exhausted the sub-element's inside the cluster
        //whose ID we parsed earlier.

        if (id == 0x0F43B675)  //Cluster ID
            return 0;  //no entries found

        if (id == 0x0C53BB6B)  //Cues ID
            return 0;  //no entries found

        pos += len;  //consume id field

        if ((cluster_stop >= 0) && (pos >= cluster_stop))
            return E_FILE_FORMAT_INVALID;

        //read size field

        if ((pos + 1) > avail)
        {
            len = 1;
            return E_BUFFER_NOT_FULL;
        }

        result = GetUIntLength(pReader, pos, len);

        if (result < 0)  //error
            return static_cast<long>(result);

        if (result > 0)  //underflow
            return E_BUFFER_NOT_FULL;

        if ((cluster_stop >= 0) && ((pos + len) > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if ((pos + len) > avail)
            return E_BUFFER_NOT_FULL;

        const long long size = ReadUInt(pReader, pos, len);

        if (size < 0)  //error
            return static_cast<long>(size);

        pos += len;  //consume size field

        //pos now points to start of payload

        if ((cluster_stop >= 0) && (pos > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if (size == 0)  //weird
            continue;

        const long long unknown_size = (1LL << (7 * len)) - 1;

        if (size == unknown_size)
            return E_FILE_FORMAT_INVALID;  //not supported inside cluster

        if ((cluster_stop >= 0) && ((pos + size) > cluster_stop))
            return E_FILE_FORMAT_INVALID;

        if (id == 0x20)  //BlockGroup ID
            return 1;    //have at least one entry

        if (id == 0x23)  //SimpleBlock ID
            return 1;    //have at least one entry

        pos += size;  //consume payload
        assert((cluster_stop < 0) || (pos <= cluster_stop));
    }
}


void Cluster::LoadBlockEntries() const
{
    //LoadBlockEntries loads all of the entries on the cluster.

    //if (m_entries)
    //    return;

    //if (m_entries_count == 0)  //already parsed, and no entries found
    //    return;

    if (m_pSegment == 0)  //EOS cluster
        return;

    assert(m_pos >= m_element_start);
    //assert(m_size);  //preloaded only, or (partially) loaded
    //assert(m_entries_count < 0);

    IMkvReader* const pReader = m_pSegment->m_pReader;

    //if (m_pos < 0)
    //    m_pos *= -1;  //relative to segment
    //long long pos = m_pSegment->m_start + m_pos;  //absolute

    if (m_element_size < 0)
    {
        assert(m_pos == m_element_start);

        long len;

        const long long id = ReadUInt(pReader, m_pos, len);
        id;
        assert(id >= 0);
        assert(id == 0x0F43B675);  //Cluster ID

        m_pos += len;  //consume id

        const long long cluster_size = ReadUInt(pReader, m_pos, len);
        assert(cluster_size > 0);

        const long long unknown_size = (1LL << (7 * len)) - 1;
        unknown_size;
        assert(cluster_size != unknown_size);

        m_pos += len;  //consume size field

        //m_pos now points to start of cluster payload

        const long long cluster_stop = m_pos + cluster_size;
        const long long element_size = cluster_stop - m_element_start;
        assert((m_element_size <= 0) || (m_element_size == element_size));

        if (m_element_size <= 0)
            m_element_size = element_size;
    }

    //assert(m_size > 0);
    //assert(m_element_size > m_size);

    const long long cluster_stop = m_element_start + m_element_size;

    if (m_pos >= cluster_stop)
        return;

    long long timecode = -1;  //of cluster itself

    //First count the number of entries (that remain)

    long long pos = m_pos;
    int entries_count = 0;  //that remain

    while (pos < cluster_stop)
    {
        if (Match(pReader, pos, 0x67, timecode))
        {
            if (m_timecode >= 0)
                assert(timecode == m_timecode);
            else
                m_timecode = timecode;
        }
        else
        {
            long len;

            const long long id = ReadUInt(pReader, pos, len);
            assert(id >= 0);  //TODO
            assert((pos + len) <= cluster_stop);

            pos += len;  //consume id

            const long long size = ReadUInt(pReader, pos, len);
            assert(size >= 0);  //TODO
            assert((pos + len) <= cluster_stop);

            pos += len;  //consume size

            if (id == 0x20)  //BlockGroup ID
                ++entries_count;
            else if (id == 0x23)  //SimpleBlock ID
                ++entries_count;

            pos += size;  //consume payload
            assert(pos <= cluster_stop);
        }
    }

    assert(pos == cluster_stop);
    assert(m_timecode >= 0);

    if (entries_count == 0)  //nothing remains to be done
    {
        m_pos = pos;

        if (m_entries_count < 0)
            m_entries_count = 0;

        return;
    }

    BlockEntry** ppEntry;

    if (m_entries_count < 0)  //haven't parsed anything yet
    {
        assert(m_entries == NULL);
        assert(m_entries_size == 0);

        m_entries_size = entries_count;
        m_entries = new BlockEntry*[m_entries_size];

        ppEntry = m_entries;
        m_entries_count = entries_count;
    }
    else
    {
        assert(m_entries);
        assert(m_entries_size > 0);
        assert(m_entries_count > 0);
        assert(m_entries_count <= m_entries_size);

        const long entries_size = m_entries_count + entries_count;

        if (m_entries_size < entries_size)
        {
            BlockEntry** const entries = new BlockEntry*[entries_size];
            assert(entries);

            BlockEntry** src = m_entries;
            BlockEntry** const src_end = src + m_entries_count;

            BlockEntry** dst = entries;

            while (src != src_end)
                *dst++ = *src++;

            delete[] m_entries;

            m_entries = entries;
            m_entries_size = entries_size;
        }

        ppEntry = m_entries + m_entries_count;
        m_entries_count = entries_size;
    }

    while (m_pos < cluster_stop)
    {
        long len;
        const long long id = ReadUInt(pReader, m_pos, len);
        assert(id >= 0);  //TODO
        assert((m_pos + len) <= cluster_stop);

        m_pos += len;  //consume id

        const long long size = ReadUInt(pReader, m_pos, len);
        assert(size >= 0);  //TODO
        assert((m_pos + len) <= cluster_stop);

        m_pos += len;  //consume size

        if (id == 0x20)  //BlockGroup ID
            CreateBlockGroup(m_pos, size, ppEntry);
        else if (id == 0x23)  //SimpleBlock ID
            CreateSimpleBlock(m_pos, size, ppEntry);

        m_pos += size;  //consume payload
        assert(m_pos <= cluster_stop);
    }

    assert(m_pos == cluster_stop);
    assert((ppEntry - m_entries) == m_entries_count);
}



long long Cluster::GetTimeCode() const
{
#if 0
    Load();
#else
    long long pos;
    long len;

    const long status = Load(pos, len);
    status;
    assert(status == 0);
#endif

    return m_timecode;
}


long long Cluster::GetTime() const
{
    const long long tc = GetTimeCode();
    assert(tc >= 0);

    const SegmentInfo* const pInfo = m_pSegment->GetInfo();
    assert(pInfo);

    const long long scale = pInfo->GetTimeCodeScale();
    assert(scale >= 1);

    const long long t = m_timecode * scale;

    return t;
}


long long Cluster::GetFirstTime() const
{
    const BlockEntry* const pEntry = GetFirst();

    if (pEntry == NULL)  //empty cluster
        return GetTime();

    const Block* const pBlock = pEntry->GetBlock();
    assert(pBlock);

    return pBlock->GetTime(this);
}


long long Cluster::GetLastTime() const
{
    const BlockEntry* const pEntry = GetLast();

    if (pEntry == NULL)  //empty cluster
        return GetTime();

    const Block* const pBlock = pEntry->GetBlock();
    assert(pBlock);

    return pBlock->GetTime(this);
}


void Cluster::CreateBlock(
    long long id,
    long long pos,   //absolute pos of payload
    long long size) const
{
    BlockEntry** ppEntry;

    if (m_entries_count < 0)  //haven't parsed anything yet
    {
        assert(m_entries == NULL);
        assert(m_entries_size == 0);

        m_entries_size = 1024;
        m_entries = new BlockEntry*[m_entries_size];

        ppEntry = m_entries;
        m_entries_count = 1;
    }
    else
    {
        assert(m_entries);
        assert(m_entries_size > 0);
        assert(m_entries_count > 0);
        assert(m_entries_count <= m_entries_size);

        if (m_entries_count >= m_entries_size)
        {
            const long entries_size = 2 * m_entries_size;

            BlockEntry** const entries = new BlockEntry*[entries_size];
            assert(entries);

            BlockEntry** src = m_entries;
            BlockEntry** const src_end = src + m_entries_count;

            BlockEntry** dst = entries;

            while (src != src_end)
                *dst++ = *src++;

            delete[] m_entries;

            m_entries = entries;
            m_entries_size = entries_size;
        }

        ppEntry = m_entries + m_entries_count;
        ++m_entries_count;
    }

    if (id == 0x20)  //BlockGroup ID
        CreateBlockGroup(pos, size, ppEntry);
    else
    {
        assert(id == 0x23);  //SimpleBlock ID
        CreateSimpleBlock(pos, size, ppEntry);
    }
}


void Cluster::CreateBlockGroup(
    long long st,
    long long sz,
    BlockEntry**& ppEntry) const
{
    assert(m_entries);
    assert(m_entries_size > 0);
    assert(ppEntry);
    assert(ppEntry >= m_entries);

    const ptrdiff_t idx = ppEntry - m_entries;
    assert(idx >= 0);
    assert(idx < m_entries_size);

    Cluster* const this_ = const_cast<Cluster*>(this);
    *ppEntry++ = new BlockGroup(this_, idx, st, sz);
}



void Cluster::CreateSimpleBlock(
    long long st,
    long long sz,
    BlockEntry**& ppEntry) const
{
    assert(m_entries);
    assert(m_entries_size > 0);
    assert(ppEntry);
    assert(ppEntry >= m_entries);

    const ptrdiff_t idx = ppEntry - m_entries;
    assert(idx >= 0);
    assert(idx < m_entries_size);

    Cluster* const this_ = const_cast<Cluster*>(this);
    *ppEntry++ = new SimpleBlock(this_, idx, st, sz);
}


const BlockEntry* Cluster::GetFirst() const
{
    LoadBlockEntries();

    if ((m_entries == NULL) || (m_entries_count <= 0))
        return NULL;

    const BlockEntry* const pFirst = m_entries[0];
    assert(pFirst);

    return pFirst;
}


const BlockEntry* Cluster::GetLast() const
{
    LoadBlockEntries();

    if ((m_entries == NULL) || (m_entries_count <= 0))
        return NULL;

    const long idx = m_entries_count - 1;

    const BlockEntry* const pLast = m_entries[idx];
    assert(pLast);

    return pLast;
}


const BlockEntry* Cluster::GetNext(const BlockEntry* pEntry) const
{
    assert(pEntry);
    assert(m_entries != NULL);
    assert(m_entries_count > 0);

    size_t idx = pEntry->GetIndex();
    assert(idx < size_t(m_entries_count));
    assert(m_entries[idx] == pEntry);

    ++idx;

    if (idx >= size_t(m_entries_count))
      return NULL;

    return m_entries[idx];
}


long Cluster::GetEntryCount() const
{
    return m_entries_count;
}


const BlockEntry* Cluster::GetEntry(
    const Track* pTrack,
    long long time_ns) const
{
    assert(pTrack);

    if (m_pSegment == NULL)  //this is the special EOS cluster
        return pTrack->GetEOS();

    LoadBlockEntries();

    if ((m_entries == NULL) || (m_entries_count <= 0))
        return NULL;  //return EOS here?

    const BlockEntry* pResult = pTrack->GetEOS();

    BlockEntry** i = m_entries;
    assert(i);

    BlockEntry** const j = i + m_entries_count;

    while (i != j)
    {
        const BlockEntry* const pEntry = *i++;
        assert(pEntry);
        assert(!pEntry->EOS());

        const Block* const pBlock = pEntry->GetBlock();
        assert(pBlock);

        if (pBlock->GetTrackNumber() != pTrack->GetNumber())
            continue;

        if (pTrack->VetEntry(pEntry))
        {
            if (time_ns < 0)  //just want first candidate block
                return pEntry;

            const long long ns = pBlock->GetTime(this);

            if (ns > time_ns)
                break;

            pResult = pEntry;
        }
        else if (time_ns >= 0)
        {
            const long long ns = pBlock->GetTime(this);

            if (ns > time_ns)
                break;
        }
    }

    return pResult;
}


const BlockEntry*
Cluster::GetEntry(
    const CuePoint& cp,
    const CuePoint::TrackPosition& tp) const
{
    assert(m_pSegment);

    LoadBlockEntries();

    if (m_entries == NULL)
        return NULL;

    const long long count = m_entries_count;

    if (count <= 0)
        return NULL;

    const long long tc = cp.GetTimeCode();

    if ((tp.m_block > 0) && (tp.m_block <= count))
    {
        const size_t block = static_cast<size_t>(tp.m_block);
        const size_t index = block - 1;

        const BlockEntry* const pEntry = m_entries[index];
        assert(pEntry);
        assert(!pEntry->EOS());

        const Block* const pBlock = pEntry->GetBlock();
        assert(pBlock);

        if ((pBlock->GetTrackNumber() == tp.m_track) &&
            (pBlock->GetTimeCode(this) == tc))
        {
            return pEntry;
        }
    }

    const BlockEntry* const* i = m_entries;
    const BlockEntry* const* const j = i + count;

    while (i != j)
    {
#ifdef _DEBUG
        const ptrdiff_t idx = i - m_entries;
        idx;
#endif

        const BlockEntry* const pEntry = *i++;
        assert(pEntry);
        assert(!pEntry->EOS());

        const Block* const pBlock = pEntry->GetBlock();
        assert(pBlock);

        if (pBlock->GetTrackNumber() != tp.m_track)
            continue;

        const long long tc_ = pBlock->GetTimeCode(this);
        assert(tc_ >= 0);

        if (tc_ < tc)
            continue;

        if (tc_ > tc)
            return NULL;

        const Tracks* const pTracks = m_pSegment->GetTracks();
        assert(pTracks);

        const long tn = static_cast<long>(tp.m_track);
        const Track* const pTrack = pTracks->GetTrackByNumber(tn);

        if (pTrack == NULL)
            return NULL;

        const long long type = pTrack->GetType();

        if (type == 2)  //audio
            return pEntry;

        if (type != 1)  //not video
            return NULL;

        if (!pBlock->IsKey())
            return NULL;

        return pEntry;
    }

    return NULL;
}


const BlockEntry* Cluster::GetMaxKey(const VideoTrack* pTrack) const
{
    assert(pTrack);

    if (m_pSegment == NULL)  //EOS
        return pTrack->GetEOS();

    LoadBlockEntries();

    if ((m_entries == NULL) || (m_entries_count <= 0))
        return pTrack->GetEOS();

    BlockEntry** i = m_entries + m_entries_count;
    BlockEntry** const j = m_entries;

    while (i != j)
    {
        const BlockEntry* const pEntry = *--i;
        assert(pEntry);
        assert(!pEntry->EOS());

        const Block* const pBlock = pEntry->GetBlock();
        assert(pBlock);

        if (pBlock->GetTrackNumber() != pTrack->GetNumber())
            continue;

        if (pBlock->IsKey())
            return pEntry;
    }

    return pTrack->GetEOS();  //no satisfactory block found
}



BlockEntry::BlockEntry()
{
}


BlockEntry::~BlockEntry()
{
}


SimpleBlock::SimpleBlock(
    Cluster* pCluster,
    size_t idx,
    long long start,
    long long size) :
    m_pCluster(pCluster),
    m_index(idx),
    m_block(start, size, pCluster->m_pSegment->m_pReader)
{
}


bool SimpleBlock::EOS() const
{
    return false;
}


const Cluster* SimpleBlock::GetCluster() const
{
    return m_pCluster;
}


size_t SimpleBlock::GetIndex() const
{
    return m_index;
}


const Block* SimpleBlock::GetBlock() const
{
    return &m_block;
}


//bool SimpleBlock::IsBFrame() const
//{
//    return false;
//}


BlockGroup::BlockGroup(
    Cluster* pCluster,
    size_t idx,
    long long start,
    long long size_) :
    m_pCluster(pCluster),
    m_index(idx),
    m_prevTimeCode(0),
    m_nextTimeCode(0),
    m_pBlock(NULL)  //TODO: accept multiple blocks within a block group
{
    IMkvReader* const pReader = m_pCluster->m_pSegment->m_pReader;

    long long pos = start;
    const long long stop = start + size_;

    bool bSimpleBlock = false;
    bool bReferenceBlock = false;

    while (pos < stop)
    {
        short t;

        if (Match(pReader, pos, 0x7B, t))
        {
            if (t < 0)
                m_prevTimeCode = t;
            else if (t > 0)
                m_nextTimeCode = t;
            else
                assert(false);

            bReferenceBlock = true;
        }
        else
        {
            long len;
            const long long id = ReadUInt(pReader, pos, len);
            assert(id >= 0);  //TODO
            assert((pos + len) <= stop);

            pos += len;  //consume ID

            const long long size = ReadUInt(pReader, pos, len);
            assert(size >= 0);  //TODO
            assert((pos + len) <= stop);

            pos += len;  //consume size

            switch (id)
            {
                case 0x23:  //SimpleBlock ID
                    bSimpleBlock = true;
                    //YES, FALL THROUGH TO NEXT CASE

                case 0x21:  //Block ID
                    ParseBlock(pos, size);
                    break;

                default:
                    break;
            }

            pos += size;  //consume payload
            assert(pos <= stop);
        }
    }

    assert(pos == stop);
    assert(m_pBlock);

    if (!bSimpleBlock)
        m_pBlock->SetKey(!bReferenceBlock);
}


BlockGroup::~BlockGroup()
{
    delete m_pBlock;
}


void BlockGroup::ParseBlock(long long start, long long size)
{
    IMkvReader* const pReader = m_pCluster->m_pSegment->m_pReader;

    Block* const pBlock = new Block(start, size, pReader);
    assert(pBlock);  //TODO

    //TODO: the Matroska spec says you have multiple blocks within the
    //same block group, with blocks ranked by priority (the flag bits).

    assert(m_pBlock == NULL);
    m_pBlock = pBlock;
}


bool BlockGroup::EOS() const
{
    return false;
}


const Cluster* BlockGroup::GetCluster() const
{
    return m_pCluster;
}


size_t BlockGroup::GetIndex() const
{
    return m_index;
}


const Block* BlockGroup::GetBlock() const
{
    return m_pBlock;
}


short BlockGroup::GetPrevTimeCode() const
{
    return m_prevTimeCode;
}


short BlockGroup::GetNextTimeCode() const
{
    return m_nextTimeCode;
}


//bool BlockGroup::IsBFrame() const
//{
//    return (m_nextTimeCode > 0);
//}


Block::Block(long long start, long long size_, IMkvReader* pReader) :
    m_start(start),
    m_size(size_)
{
    long long pos = start;
    const long long stop = start + size_;

    long len;

    m_track = ReadUInt(pReader, pos, len);
    assert(m_track > 0);
    assert((pos + len) <= stop);

    pos += len;  //consume track number
    assert((stop - pos) >= 2);

    m_timecode = Unserialize2SInt(pReader, pos);

    pos += 2;
    assert((stop - pos) >= 1);

    long status = pReader->Read(pos, 1, &m_flags);
    assert(status == 0);

#if 0
    const int invisible = int(m_flags & 0x08) >> 3;
    invisible;
    assert(!invisible);  //TODO
#endif

    const int lacing = int(m_flags & 0x06) >> 1;

    ++pos;  //consume flags byte
    assert(pos <= stop);

    if (lacing == 0)  //no lacing
    {
        m_frame_count = 1;
        m_frames = new Frame[m_frame_count];

        Frame& f = m_frames[0];
        f.pos = pos;

        const long long frame_size = stop - pos;
        assert(frame_size <= LONG_MAX);

        f.len = static_cast<long>(frame_size);

        return;
    }

    assert(pos < stop);

    unsigned char count;

    status = pReader->Read(pos, 1, &count);
    assert(status == 0);

    ++pos;  //consume frame count
    assert(pos <= stop);

    m_frame_count = ++count;
    m_frames = new Frame[m_frame_count];

    if (lacing == 1)  //Xiph
    {
        Frame* pf = m_frames;
        Frame* const pf_end = pf + m_frame_count;

        long size = 0;

        while (count > 1)
        {
            long frame_size = 0;

            for (;;)
            {
                unsigned char val;

                status = pReader->Read(pos, 1, &val);
                assert(status == 0);

                ++pos;  //consume xiph size byte

                frame_size += val;

                if (val < 255)
                    break;
            }

            Frame& f = *pf++;
            assert(pf < pf_end);

            f.len = frame_size;
            size += frame_size;  //contribution of this frame

            --count;
        }

        assert(pf < pf_end);
        assert(pos < stop);

        {
            Frame& f = *pf++;
            assert(pf == pf_end);

            const long long total_size = stop - pos;
            assert(total_size > size);

            const long long frame_size = total_size - size;
            assert(frame_size <= LONG_MAX);

            f.len = static_cast<long>(frame_size);
        }

        pf = m_frames;
        while (pf != pf_end)
        {
            Frame& f = *pf++;
            assert((pos + f.len) <= stop);

            f.pos = pos;
            pos += f.len;
        }

        assert(pos == stop);
    }
    else if (lacing == 2)  //fixed-size lacing
    {
        const long long total_size = stop - pos;
        assert((total_size % m_frame_count) == 0);

        const long long frame_size = total_size / m_frame_count;
        assert(frame_size <= LONG_MAX);

        Frame* pf = m_frames;
        Frame* const pf_end = pf + m_frame_count;

        while (pf != pf_end)
        {
            assert((pos + frame_size) <= stop);

            Frame& f = *pf++;

            f.pos = pos;
            f.len = static_cast<long>(frame_size);

            pos += frame_size;
        }

        assert(pos == stop);
    }
    else
    {
        assert(lacing == 3);  //EBML lacing
        assert(pos < stop);

        long size = 0;

        long long frame_size = ReadUInt(pReader, pos, len);
        assert(frame_size > 0);
        assert(frame_size <= LONG_MAX);
        assert((pos + len) <= stop);

        pos += len; //consume length of size of first frame
        assert((pos + frame_size) <= stop);

        Frame* pf = m_frames;
        Frame* const pf_end = pf + m_frame_count;

        {
            Frame& curr = *pf;

            curr.len = static_cast<long>(frame_size);
            size += curr.len;  //contribution of this frame
        }

        --count;

        while (count > 1)
        {
            assert(pos < stop);
            assert(pf < pf_end);

            const Frame& prev = *pf++;
            assert(pf < pf_end);
            assert(prev.len == frame_size);

            Frame& curr = *pf;

            const long long delta_size_ = ReadUInt(pReader, pos, len);
            assert(delta_size_ >= 0);
            assert((pos + len) <= stop);

            pos += len;  //consume length of (delta) size
            assert(pos <= stop);

            const int exp = 7*len - 1;
            const long long bias = (1LL << exp) - 1LL;
            const long long delta_size = delta_size_ - bias;

            frame_size += delta_size;
            assert(frame_size > 0);
            assert(frame_size <= LONG_MAX);

            curr.len = static_cast<long>(frame_size);
            size += curr.len;  //contribution of this frame

            --count;
        }

        {
            assert(pos < stop);
            assert(pf < pf_end);

            const Frame& prev = *pf++;
            assert(pf < pf_end);
            assert(prev.len == frame_size);

            Frame& curr = *pf++;
            assert(pf == pf_end);

            const long long total_size = stop - pos;
            assert(total_size > 0);
            assert(total_size > size);

            frame_size = total_size - size;
            assert(frame_size > 0);
            assert(frame_size <= LONG_MAX);

            curr.len = static_cast<long>(frame_size);
        }

        pf = m_frames;
        while (pf != pf_end)
        {
            Frame& f = *pf++;
            assert((pos + f.len) <= stop);

            f.pos = pos;
            pos += f.len;
        }

        assert(pos == stop);
    }
}


Block::~Block()
{
    delete[] m_frames;
}


long long Block::GetTimeCode(const Cluster* pCluster) const
{
    assert(pCluster);

    const long long tc0 = pCluster->GetTimeCode();
    assert(tc0 >= 0);

    const long long tc = tc0 + static_cast<long long>(m_timecode);
    assert(tc >= 0);

    return tc;  //unscaled timecode units
}


long long Block::GetTime(const Cluster* pCluster) const
{
    assert(pCluster);

    const long long tc = GetTimeCode(pCluster);

    const Segment* const pSegment = pCluster->m_pSegment;
    const SegmentInfo* const pInfo = pSegment->GetInfo();
    assert(pInfo);

    const long long scale = pInfo->GetTimeCodeScale();
    assert(scale >= 1);

    const long long ns = tc * scale;

    return ns;
}


long long Block::GetTrackNumber() const
{
    return m_track;
}


bool Block::IsKey() const
{
    return ((m_flags & static_cast<unsigned char>(1 << 7)) != 0);
}


void Block::SetKey(bool bKey)
{
    if (bKey)
        m_flags |= static_cast<unsigned char>(1 << 7);
    else
        m_flags &= 0x7F;
}


bool Block::IsInvisible() const
{
    return bool(int(m_flags & 0x08) != 0);
}


int Block::GetFrameCount() const
{
    return m_frame_count;
}


const Block::Frame& Block::GetFrame(int idx) const
{
    assert(idx >= 0);
    assert(idx < m_frame_count);

    const Frame& f = m_frames[idx];
    assert(f.pos > 0);
    assert(f.len > 0);

    return f;
}


long Block::Frame::Read(IMkvReader* pReader, unsigned char* buf) const
{
    assert(pReader);
    assert(buf);

    const long status = pReader->Read(pos, len, buf);
    return status;
}


}  //end namespace mkvparser