Generate and assign media track ids in demuxers.

third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 567 matching lines @@
 }
 
 WebVector<WebMediaPlayer::TrackId> SourceBuffer::initializationSegmentReceived(const WebVector<MediaTrackInfo>& newTracks)
 {
     DVLOG(SOURCE_BUFFER_LOG_LEVEL) << __FUNCTION__ << "(" << this << ") tracks=" << newTracks.size();
     DCHECK(m_source);
     DCHECK(m_source->mediaElement());
     DCHECK(m_updating);
 
     // TODO(servolk): Implement proper 'initialization segment received' algorithm according to MSE spec:
     // https://w3c.github.io/media-source/#sourcebuffer-init-segment-received

[wolenetz, 2016/06/09 19:20:58]

There can be an N:1 {HTMLMediaElement,SourceBuffer}.{audio,video,text}Track
entry:bytstream_parsed_track in MSE case because the "default track kinds
algorithm" can allow an app to supply multiple kinds for a matching bytestream
track. The MSE spec requires multiple HTMLME/SourceBuffer tracklist entries (1
per kind), though only 1 MSE track buffer. Consider track buffer the
demuxerstream, and the tracklist entry the one that needs a unique app-visible
|id| property. The latter can alias N:1 the former.

How does this CL envision supporting this scenario? I think we'd previously
mis-assumed a 1:1 BlinkTrack:BytestreamTrack for MSE.

[servolk, 2016/06/09 20:42:04]

Yes, I remember that there might be multiple kinds for a single media track. I
tried to explain how we could deal with that in
https://codereview.chromium.org/1922333002#msg19.
To repeat/clarify here: I think that when we do have multiple kinds, then we
could generate more unique track ids in blink by appending the '-<kind>' string
to the track id generated by the demuxer. For example, if we have a single audio
track and the demuxer assigned it a unique id that is '1', then we have 'main'
and 'alternative' kinds for that track in the TrackDefaults, then here in the
init segment handling algorithm we would add two audio tracks, one with id
'1-main' and another one with id '1-alternative'. Although to be honest I don't
fully understand how it would be useful. Why would it be useful to have multiple
tracks of different kinds if they are backed by a single bytestream on the
demuxer level? How would we handle the enabling/disabling in those cases? E.g.
in the scenario I gave above was would be the expected effect of disabling the
'1-alternative' audio track? The '1-main' is still enabled, so I guess the audio
should continue playing until all tracks corresponding to that
bytestream/demuxer track id are disabled.

     WebVector<WebMediaPlayer::TrackId> result(newTracks.size());
     unsigned resultIdx = 0;
     for (const auto& trackInfo : newTracks) {
         if (!RuntimeEnabledFeatures::audioVideoTracksEnabled()) {
-            static WebMediaPlayer::TrackId nextTrackId = 0;
-            result[resultIdx++] = ++nextTrackId;
+            static unsigned nextTrackId = 0;
+            StringBuilder stringBuilder;
+            stringBuilder.appendNumber(++nextTrackId);
+            result[resultIdx++] = stringBuilder.toString();
             continue;
         }
 
         const TrackBase* trackBase = nullptr;
         if (trackInfo.trackType == WebMediaPlayer::AudioTrack) {
             AudioTrack* audioTrack = nullptr;
             if (!m_firstInitializationSegmentReceived) {
                 audioTrack = AudioTrack::create(trackInfo.byteStreamTrackId, trackInfo.kind, trackInfo.label, trackInfo.language, false);
                 SourceBufferTrackBaseSupplement::setSourceBuffer(*audioTrack, this);
                 audioTracks().add(audioTrack);
@@ skipping 18 matching lines @@
             trackBase = videoTrack;
             result[resultIdx++] = videoTrack->trackId();
         } else {
             NOTREACHED();
         }
         (void)trackBase;
 #if !LOG_DISABLED
         const char* logActionStr = m_firstInitializationSegmentReceived ? "using existing" : "added";
         const char* logTrackTypeStr = (trackInfo.trackType == WebMediaPlayer::AudioTrack) ? "audio" : "video";
         DVLOG(SOURCE_BUFFER_LOG_LEVEL) << __FUNCTION__ << "(" << this << ") " << logActionStr << " "
-            << logTrackTypeStr << " Track " << trackBase << "trackId=" << trackBase->trackId() << " id="
-            << trackBase->id() << " label=" << trackBase->label() << " lang=" << trackBase->language();
+            << logTrackTypeStr << " Track " << trackBase << " trackId=" << (String)trackBase->trackId()
+            << " label=" << trackBase->label() << " lang=" << trackBase->language();
 #endif
     }
 
     if (!m_firstInitializationSegmentReceived) {
         // 5. If active track flag equals true, then run the following steps:
         // 5.1. Add this SourceBuffer to activeSourceBuffers.
         // 5.2. Queue a task to fire a simple event named addsourcebuffer at
         // activesourcebuffers.
         m_source->setSourceBufferActive(this);
 
@@ skipping 381 matching lines @@
     visitor->trace(m_removeAsyncPartRunner);
     visitor->trace(m_appendStreamAsyncPartRunner);
     visitor->trace(m_stream);
     visitor->trace(m_audioTracks);
     visitor->trace(m_videoTracks);
     EventTargetWithInlineData::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
 } // namespace blink