Generate and assign media track ids in demuxers.

media/filters/ffmpeg_demuxer.cc

Index: media/filters/ffmpeg_demuxer.cc
diff --git a/media/filters/ffmpeg_demuxer.cc b/media/filters/ffmpeg_demuxer.cc
index b6272fe0f3793f8215c11aa5bda53832c6e9d7bf..5f476933fc8bf653835fce72004e6fc82c4c1da3 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -1118,6 +1118,8 @@ void FFmpegDemuxer::OnFindStreamInfoDone(const PipelineStatusCB& status_cb,
   AVStream* video_stream = NULL;
   VideoDecoderConfig video_config;
 
+  DCHECK(track_id_to_demux_stream_map_.empty());
+
   // If available, |start_time_| will be set to the lowest stream start time.
   start_time_ = kInfiniteDuration();
 
@@ -1223,22 +1225,27 @@ void FFmpegDemuxer::OnFindStreamInfoDone(const PipelineStatusCB& status_cb,
 
     // Note when we find our audio/video stream (we only want one of each) and
     // record src= playback UMA stats for the stream's decoder config.
+    MediaTrack* media_track = nullptr;
     if (codec_type == AVMEDIA_TYPE_AUDIO) {
       CHECK(!audio_stream);
       audio_stream = stream;
       audio_config = streams_[i]->audio_decoder_config();
       RecordAudioCodecStats(audio_config);
 
-      media_tracks->AddAudioTrack(audio_config, track_id, "main", track_label,
-                                  track_language);
+      media_track = media_tracks->AddAudioTrack(audio_config, track_id, "main",
+                                                track_label, track_language);
+      media_track->setId(base::UintToString(track_id));

[chcunningham, 2016/06/09 17:57:19]

So for src=, we re-use the bytstream track Id to set media track id. Should be
fine since the audio and video tracks should all have unique bytstream ids. I'd
add a CHECK (to catch bugs in ffmpeg or bugs in our assumptions) that you don't
already have the track id in the map before you add the new streams below.

[servolk, 2016/06/09 19:14:46]

Done. Only I've added a DCHECK, don't think it deserves a crash. We might be
able to continue normally by just overwriting the old id.

+      track_id_to_demux_stream_map_[media_track->id()] = streams_[i];
     } else if (codec_type == AVMEDIA_TYPE_VIDEO) {
       CHECK(!video_stream);
       video_stream = stream;
       video_config = streams_[i]->video_decoder_config();
       RecordVideoCodecStats(video_config, stream->codec->color_range);
 
-      media_tracks->AddVideoTrack(video_config, track_id, "main", track_label,
-                                  track_language);
+      media_track = media_tracks->AddVideoTrack(video_config, track_id, "main",
+                                                track_label, track_language);
+      media_track->setId(base::UintToString(track_id));
+      track_id_to_demux_stream_map_[media_track->id()] = streams_[i];
     }
 
     max_duration = std::max(max_duration, streams_[i]->duration());
@@ -1419,6 +1426,13 @@ void FFmpegDemuxer::OnFindStreamInfoDone(const PipelineStatusCB& status_cb,
   status_cb.Run(PIPELINE_OK);
 }
 
+const DemuxerStream* FFmpegDemuxer::GetDemuxerStreamByTrackId(
+    MediaTrack::TrackId track_id) const {
+  auto it = track_id_to_demux_stream_map_.find(track_id);
+  DCHECK(it != track_id_to_demux_stream_map_.end());
+  return it->second;
+}
+
 void FFmpegDemuxer::OnSeekFrameDone(const PipelineStatusCB& cb, int result) {
   DCHECK(task_runner_->BelongsToCurrentThread());
   CHECK(pending_seek_);