mkvparser: create generic track objects

Formerly, it was only possible to create instances of
the Track subclasses, VideoTrack and AudioTrack.  However,
we now populate WebM files with WebVTT metadata blocks,
so we must allow for a third kind of track object.

We now enable instances of type Track to be created,
by providing a new factory function, Track::Create, and
making all Track methods non-pure and with a generic
implementation.

Change-Id: I7d4c965eb566b9fc2f5ceefe1d43723cf8c1e5f0

mkvparser.cpp

@@ -4760,6 +4760,35 @@ Track::~Track()
     delete [] content_encoding_entries_;
 }
 
+long Track::Create(
+    Segment* pSegment,
+    const Info& info,
+    long long element_start,
+    long long element_size,
+    Track*& pResult)
+{
+    if (pResult)
+        return -1;
+
+    Track* const pTrack = new (std::nothrow) Track(pSegment,
+                                                   element_start,
+                                                   element_size);
+
+    if (pTrack == NULL)
+        return -1;  //generic error
+
+    const int status = info.Copy(pTrack->m_info);
+
+    if (status)  // error
+    {
+        delete pTrack;
+        return status;
+    }
+
+    pResult = pTrack;
+    return 0;  //success
+}
+
 Track::Info::Info():
     nameAsUTF8(NULL),
     codecId(NULL),
@@ -5098,6 +5127,31 @@ long Track::GetNext(
     return 1;
 }
 
+bool Track::VetEntry(const BlockEntry* pBlockEntry) const
+{
+    assert(pBlockEntry);
+    const Block* const pBlock = pBlockEntry->GetBlock();
+    assert(pBlock);
+    assert(pBlock->GetTrackNumber() == m_info.number);
+
+    // This function is used during a seek to determine whether the
+    // frame is a valid seek target.  This default function simply
+    // returns true, which means all frames are valid seek targets.
+    // It gets overridden by the VideoTrack class, because only video
+    // keyframes can be used as seek target.
+
+    return true;
+}
+
+long Track::Seek(
+    long long /* time_ns */ ,
+    const BlockEntry*& pResult) const
+{
+    // TODO(matthewjheaney): need to implement this?
+    pResult = NULL;
+    return -1;  // generic error
+}
+
 const ContentEncoding*
 Track::GetContentEncodingByIndex(unsigned long idx) const {
   const ptrdiff_t count =
@@ -5221,15 +5275,15 @@ VideoTrack::VideoTrack(
 
 long VideoTrack::Parse(
     Segment* pSegment,
-    const Info& i,
+    const Info& info,
-    long long elem_st,
+    long long element_start,
-    long long elem_sz,
+    long long element_size,
-    VideoTrack*& pTrack)
+    VideoTrack*& pResult)
 {
-    if (pTrack)
+    if (pResult)
         return -1;
 
-    if (i.type != Track::kVideo)
+    if (info.type != Track::kVideo)
         return -1;
 
     long long width = 0;
@@ -5238,7 +5292,7 @@ long VideoTrack::Parse(
 
     IMkvReader* const pReader = pSegment->m_pReader;
 
-    const Settings& s = i.settings;
+    const Settings& s = info.settings;
     assert(s.start >= 0);
     assert(s.size >= 0);
 
@@ -5296,36 +5350,35 @@ long VideoTrack::Parse(
 
     assert(pos == stop);
 
-    pTrack = new (std::nothrow) VideoTrack(pSegment, elem_st, elem_sz);
+    VideoTrack* const pTrack = new (std::nothrow) VideoTrack(pSegment,
+                                                             element_start,
+                                                             element_size);
 
     if (pTrack == NULL)
         return -1;  //generic error
 
-    const int status = i.Copy(pTrack->m_info);
+    const int status = info.Copy(pTrack->m_info);
 
-    if (status)
+    if (status)  // error
+    {
+        delete pTrack;
         return status;
+    }
 
     pTrack->m_width = width;
     pTrack->m_height = height;
     pTrack->m_rate = rate;
 
+    pResult = pTrack;
     return 0;  //success
 }
 
 
 bool VideoTrack::VetEntry(const BlockEntry* pBlockEntry) const
 {
-    assert(pBlockEntry);
+    return Track::VetEntry(pBlockEntry) && pBlockEntry->GetBlock()->IsKey();
-
-    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
@@ -5459,20 +5512,20 @@ AudioTrack::AudioTrack(
 
 long AudioTrack::Parse(
     Segment* pSegment,
-    const Info& i,
+    const Info& info,
-    long long elem_st,
+    long long element_start,
-    long long elem_sz,
+    long long element_size,
-    AudioTrack*& pTrack)
+    AudioTrack*& pResult)
 {
-    if (pTrack)
+    if (pResult)
         return -1;
 
-    if (i.type != Track::kAudio)
+    if (info.type != Track::kAudio)
         return -1;
 
     IMkvReader* const pReader = pSegment->m_pReader;
 
-    const Settings& s = i.settings;
+    const Settings& s = info.settings;
     assert(s.start >= 0);
     assert(s.size >= 0);
 
@@ -5481,7 +5534,7 @@ long AudioTrack::Parse(
 
     const long long stop = pos + s.size;
 
-    double rate = 8000.0;
+    double rate = 8000.0;  // MKV default
     long long channels = 1;
     long long bit_depth = 0;
 
@@ -5530,36 +5583,30 @@ long AudioTrack::Parse(
 
     assert(pos == stop);
 
-    pTrack = new (std::nothrow) AudioTrack(pSegment, elem_st, elem_sz);
+    AudioTrack* const pTrack = new (std::nothrow) AudioTrack(pSegment,
+                                                             element_start,
+                                                             element_size);
 
     if (pTrack == NULL)
         return -1;  //generic error
 
-    const int status = i.Copy(pTrack->m_info);
+    const int status = info.Copy(pTrack->m_info);
 
     if (status)
+    {
+        delete pTrack;
         return status;
+    }
 
     pTrack->m_rate = rate;
     pTrack->m_channels = channels;
     pTrack->m_bitDepth = bit_depth;
 
+    pResult = pTrack;
     return 0;  //success
 }
 
 
-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
@@ -5791,11 +5838,11 @@ unsigned long Tracks::GetTracksCount() const
 long Tracks::ParseTrackEntry(
     long long track_start,
     long long track_size,
-    long long elem_st,
+    long long element_start,
-    long long elem_sz,
+    long long element_size,
-    Track*& pTrack) const
+    Track*& pResult) const
 {
-    if (pTrack)
+    if (pResult)
         return -1;
 
     IMkvReader* const pReader = m_pSegment->m_pReader;
@@ -5803,11 +5850,11 @@ long Tracks::ParseTrackEntry(
     long long pos = track_start;
     const long long track_stop = track_start + track_size;
 
-    Track::Info i;
+    Track::Info info;
 
-    i.type = 0;
+    info.type = 0;
-    i.number = 0;
+    info.number = 0;
-    i.uid = 0;
+    info.uid = 0;
 
     Track::Settings v;
     v.start = -1;
@@ -5868,7 +5915,7 @@ long Tracks::ParseTrackEntry(
             if ((size <= 0) || (size > 8))
                 return E_FILE_FORMAT_INVALID;
 
-            i.uid = 0;
+            info.uid = 0;
 
             long long pos_ = start;
             const long long pos_end = start + size;
@@ -5882,8 +5929,8 @@ long Tracks::ParseTrackEntry(
                 if (status)
                     return status;
 
-                i.uid <<= 8;
+                info.uid <<= 8;
-                i.uid |= b;
+                info.uid |= b;
 
                 ++pos_;
             }
@@ -5895,7 +5942,7 @@ long Tracks::ParseTrackEntry(
             if ((num <= 0) || (num > 127))
                 return E_FILE_FORMAT_INVALID;
 
-            i.number = static_cast<long>(num);
+            info.number = static_cast<long>(num);
         }
         else if (id == 0x03)  //Track Type
         {
@@ -5904,7 +5951,7 @@ long Tracks::ParseTrackEntry(
             if ((type <= 0) || (type > 254))
                 return E_FILE_FORMAT_INVALID;
 
-            i.type = static_cast<long>(type);
+            info.type = static_cast<long>(type);
         }
         else if (id == 0x136E)  //Track Name
         {
@@ -5912,7 +5959,7 @@ long Tracks::ParseTrackEntry(
                                     pReader,
                                     pos,
                                     size,
-                                    i.nameAsUTF8);
+                                    info.nameAsUTF8);
 
             if (status)
                 return status;
@@ -5923,7 +5970,7 @@ long Tracks::ParseTrackEntry(
                                     pReader,
                                     pos,
                                     size,
-                                    i.codecId);
+                                    info.codecId);
 
             if (status)
                 return status;
@@ -5937,9 +5984,9 @@ long Tracks::ParseTrackEntry(
         }
         else if (id == 0x23A2)  //Codec Private
         {
-            delete[] i.codecPrivate;
+            delete[] info.codecPrivate;
-            i.codecPrivate = NULL;
+            info.codecPrivate = NULL;
-            i.codecPrivateSize = 0;
+            info.codecPrivateSize = 0;
 
             if (size <= 0)
                 return E_FILE_FORMAT_INVALID;
@@ -5961,8 +6008,8 @@ long Tracks::ParseTrackEntry(
                 return status;
             }
 
-            i.codecPrivate = buf;
+            info.codecPrivate = buf;
-            i.codecPrivateSize = buflen;
+            info.codecPrivateSize = buflen;
         }
         else if (id == 0x058688)  //Codec Name
         {
@@ -5970,7 +6017,7 @@ long Tracks::ParseTrackEntry(
                                     pReader,
                                     pos,
                                     size,
-                                    i.codecNameAsUTF8);
+                                    info.codecNameAsUTF8);
 
             if (status)
                 return status;
@@ -5982,29 +6029,18 @@ long Tracks::ParseTrackEntry(
 
     assert(pos == track_stop);
 
-    if (i.number <= 0)  //not specified
+    if (info.number <= 0)  //not specified
         return E_FILE_FORMAT_INVALID;
 
-    if (GetTrackByNumber(i.number))
+    if (GetTrackByNumber(info.number))
         return E_FILE_FORMAT_INVALID;
 
-    if (i.type <= 0)  //not specified
+    if (info.type <= 0)  //not specified
         return E_FILE_FORMAT_INVALID;
 
-    if ((i.type != Track::kVideo) && (i.type != Track::kAudio))
+    info.lacing = (lacing > 0) ? true : false;
-    {
-        //TODO(matthewjheaney): go ahead and create a "generic" track
-        //object, so that GetTrackByXXX always returns something, even
-        //if the object it returns has a type that is not kVideo or kAudio.
 
-        return 0;  //no error
+    if (info.type == Track::kVideo)
-    }
-
-    i.lacing = (lacing > 0) ? true : false;
-
-    long status;
-
-    if (i.type == Track::kVideo)
     {
         if (v.start < 0)
             return E_FILE_FORMAT_INVALID;
@@ -6012,38 +6048,82 @@ long Tracks::ParseTrackEntry(
         if (a.start >= 0)
             return E_FILE_FORMAT_INVALID;
 
-        i.settings = v;
+        info.settings = v;
 
-        VideoTrack* p = NULL;
+        VideoTrack* pTrack = NULL;
 
-        status = VideoTrack::Parse(m_pSegment, i, elem_st, elem_sz, p);
+        const long status = VideoTrack::Parse(m_pSegment,
-        pTrack = p;
+                                              info,
+                                              element_start,
+                                              element_size,
+                                              pTrack);
+
+        if (status)
+            return status;
+
+        pResult = pTrack;
+        assert(pResult);
+
+        if (e.start >= 0)
+            pResult->ParseContentEncodingsEntry(e.start, e.size);
     }
-    else
+    else if (info.type == Track::kAudio)
     {
-        assert(i.type == Track::kAudio);
-
         if (a.start < 0)
             return E_FILE_FORMAT_INVALID;
 
         if (v.start >= 0)
             return E_FILE_FORMAT_INVALID;
 
-        i.settings = a;
+        info.settings = a;
 
-        AudioTrack* p = NULL;
+        AudioTrack* pTrack = NULL;
 
-        status = AudioTrack::Parse(m_pSegment, i, elem_st, elem_sz, p);
+        const long status = AudioTrack::Parse(m_pSegment,
-        pTrack = p;
+                                              info,
-    }
+                                              element_start,
+                                              element_size,
+                                              pTrack);
 
         if (status)
             return status;
 
-    assert(pTrack);
+        pResult = pTrack;
+        assert(pResult);
 
         if (e.start >= 0)
-        pTrack->ParseContentEncodingsEntry(e.start, e.size);
+            pResult->ParseContentEncodingsEntry(e.start, e.size);
+    }
+    else
+    {
+        // neither video nor audio - probably metadata
+
+        if (a.start >= 0)
+            return E_FILE_FORMAT_INVALID;
+
+        if (v.start >= 0)
+            return E_FILE_FORMAT_INVALID;
+
+        if (e.start >= 0)
+            return E_FILE_FORMAT_INVALID;
+
+        info.settings.start = -1;
+        info.settings.size = 0;
+
+        Track* pTrack = NULL;
+
+        const long status = Track::Create(m_pSegment,
+                                          info,
+                                          element_start,
+                                          element_size,
+                                          pTrack);
+
+        if (status)
+            return status;
+
+        pResult = pTrack;
+        assert(pResult);
+    }
 
     return 0;  //success
 }

mkvparser.hpp

@@ -315,6 +315,14 @@ class Track
     Track& operator=(const Track&);
 
 public:
+    class Info;
+    static long Create(
+        Segment*,
+        const Info&,
+        long long element_start,
+        long long element_size,
+        Track*&);
+
     enum Type { kVideo = 1, kAudio = 2 };
 
     Segment* const m_pSegment;
@@ -366,8 +374,8 @@ public:
 
     long GetFirst(const BlockEntry*&) const;
     long GetNext(const BlockEntry* pCurr, const BlockEntry*& pNext) const;
-    virtual bool VetEntry(const BlockEntry*) const = 0;
+    virtual bool VetEntry(const BlockEntry*) const;
-    virtual long Seek(long long time_ns, const BlockEntry*&) const = 0;
+    virtual long Seek(long long time_ns, const BlockEntry*&) const;
 
     const ContentEncoding* GetContentEncodingByIndex(unsigned long idx) const;
     unsigned long GetContentEncodingCount() const;
@@ -452,7 +460,6 @@ public:
     double GetSamplingRate() const;
     long long GetChannels() const;
     long long GetBitDepth() const;
-    bool VetEntry(const BlockEntry*) const;
     long Seek(long long time_ns, const BlockEntry*&) const;
 
 private: