Add support for WebVTT cue identifier line

Modified the mkvmuxer to write the ChapterStringUID
sub-element of the Chapter Atom element.

Modified the mkvparser to read the ChapterStringUID
sub-element of the chapter atom.

Modified the vttdemux app to write the Cue Identifier
line of the WebVTT cue.

Change-Id: I06fe386f44897ada3fe10cbf89096df104dcf779

mkvmuxer.cpp

@@ -1126,7 +1126,7 @@ bool Chapter::ExpandDisplaysArray() {
 
 uint64 Chapter::WriteAtom(IMkvWriter* writer) const {
   uint64 payload_size =
-      // TODO(matthewjheaney): resolve ID issue
+      EbmlElementSize(kMkvChapterStringUID, id_) +
       EbmlElementSize(kMkvChapterUID, uid_) +
       EbmlElementSize(kMkvChapterTimeStart, start_timecode_) +
       EbmlElementSize(kMkvChapterTimeEnd, end_timecode_);
@@ -1148,6 +1148,9 @@ uint64 Chapter::WriteAtom(IMkvWriter* writer) const {
   if (!WriteEbmlMasterElement(writer, kMkvChapterAtom, payload_size))
     return 0;
 
+  if (!WriteEbmlElement(writer, kMkvChapterStringUID, id_))
+    return 0;
+
   if (!WriteEbmlElement(writer, kMkvChapterUID, uid_))
     return 0;
 

mkvparser.cpp

@@ -4514,6 +4514,18 @@ Chapters::Atom::~Atom()
 }
 
 
+unsigned long long Chapters::Atom::GetUID() const
+{
+    return m_uid;
+}
+
+
+const char* Chapters::Atom::GetStringUID() const
+{
+    return m_string_uid;
+}
+
+
 long long Chapters::Atom::GetStartTimecode() const
 {
     return m_start_timecode;
@@ -4558,6 +4570,7 @@ const Chapters::Display* Chapters::Atom::GetDisplay(int index) const
 
 void Chapters::Atom::Init()
 {
+    m_string_uid = NULL;
     m_uid = 0;
     m_start_timecode = -1;
     m_stop_timecode = -1;
@@ -4570,6 +4583,7 @@ void Chapters::Atom::Init()
 
 void Chapters::Atom::ShallowCopy(Atom& rhs) const
 {
+    rhs.m_string_uid = m_string_uid;
     rhs.m_uid = m_uid;
     rhs.m_start_timecode = m_start_timecode;
     rhs.m_stop_timecode = m_stop_timecode;
@@ -4582,6 +4596,9 @@ void Chapters::Atom::ShallowCopy(Atom& rhs) const
 
 void Chapters::Atom::Clear()
 {
+    delete[] m_string_uid;
+    m_string_uid = NULL;
+
     while (m_displays_count > 0)
     {
         Display& d = m_displays[--m_displays_count];
@@ -4626,6 +4643,13 @@ long Chapters::Atom::Parse(
             if (status < 0)  // error
                 return status;
         }
+        else if (id == 0x1654)  // StringUID ID
+        {
+            status = UnserializeString(pReader, pos, size, m_string_uid);
+
+            if (status < 0)  // error
+                return status;
+        }
         else if (id == 0x33C4)  // UID ID
         {
             const long long val = UnserializeUInt(pReader, pos, size);

mkvparser.hpp

@@ -567,10 +567,15 @@ public:
         ~Atom();
         Atom& operator=(const Atom&);
     public:
+        unsigned long long GetUID() const;
+        const char* GetStringUID() const;
+
         long long GetStartTimecode() const;
         long long GetStopTimecode() const;
+
         long long GetStartTime(const Chapters*) const;
         long long GetStopTime(const Chapters*) const;
+
         int GetDisplayCount() const;
         const Display* GetDisplay(int index) const;
     private:
@@ -583,8 +588,8 @@ public:
         long ParseDisplay(IMkvReader*, long long pos, long long size);
         bool ExpandDisplaysArray();
 
+        char* m_string_uid;
         unsigned long long m_uid;
-        // TODO(matthewjheaney): Cue Identifier (string)
         long long m_start_timecode;
         long long m_stop_timecode;
 

vttdemux.cc

@@ -146,6 +146,12 @@ bool WriteChaptersCue(
     const mkvparser::Chapters::Atom* atom,
     const mkvparser::Chapters::Display* display);
 
+// Write the Cue Identifier line of the WebVTT cue, if it's present.
+// Returns false on error.
+bool WriteChaptersCueIdentifier(
+    FILE* file,
+    const mkvparser::Chapters::Atom* atom);
+
 // Use the timecodes from the chapters |atom| to write just the
 // timings line of the WebVTT cue.  Returns false on error.
 bool WriteChaptersCueTimings(
@@ -722,9 +728,8 @@ bool vttdemux::WriteChaptersCue(
   // the cue timings, followed by the payload of the cue.  We write
   // each part of the cue in sequence.
 
-  // TODO(matthewjheaney): write cue identifier
-  // if (!WriteChaptersCueIdentifier(f, atom))
-  //   return false;
+  if (!WriteChaptersCueIdentifier(f, atom))
+    return false;
 
   if (!WriteChaptersCueTimings(f, chapters, atom))
     return false;
@@ -735,6 +740,21 @@ bool vttdemux::WriteChaptersCue(
   return true;
 }
 
+bool vttdemux::WriteChaptersCueIdentifier(
+    FILE* f,
+    const mkvparser::Chapters::Atom* atom) {
+
+  const char* const identifier = atom->GetStringUID();
+
+  if (identifier == NULL)
+    return true;  // nothing else to do
+
+  if (fprintf(f, "%s\n", identifier) < 0)
+    return false;
+
+  return true;
+}
+
 bool vttdemux::WriteChaptersCueTimings(
     FILE* f,
     const mkvparser::Chapters* chapters,

webmids.hpp

@@ -118,6 +118,7 @@ enum MkvId {
   kMkvEditionEntry            = 0x45B9,
   kMkvChapterAtom             = 0xB6,
   kMkvChapterUID              = 0x73C4,
+  kMkvChapterStringUID        = 0x5654,
   kMkvChapterTimeStart        = 0x91,
   kMkvChapterTimeEnd          = 0x92,
   kMkvChapterDisplay          = 0x80,