Implement mapping blink track id to demuxer streams

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 6cdc56b3801e88eef3657f7cbaf151673f3dd8cd..0a4dad5c54666414aeb0227aec7e57c5206f9fd5 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -1222,22 +1222,25 @@ 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.
+    const 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_tracks->SetDemuxerStreamForMediaTrack(media_track, 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_tracks->SetDemuxerStreamForMediaTrack(media_track, streams_[i]);
     }
 
     max_duration = std::max(max_duration, streams_[i]->duration());
@@ -1596,4 +1599,17 @@ void FFmpegDemuxer::SetLiveness(DemuxerStream::Liveness liveness) {
   }
 }
 
+void FFmpegDemuxer::OnTrackIdsAssigned(const MediaTracks& tracks,
+                                       const std::vector<unsigned>& track_ids) {
+  DCHECK(track_id_to_demux_stream_.empty());

[chcunningham, 2016/06/02 21:24:45]

Same question about DCHECK vs CHECK for these two methods

[servolk, 2016/06/02 23:53:11]

It's the same here. In release build we could bypass this dcheck and overwrite
the mapping and it would work fine (although it shouldn't happen, since
FFmpegDemuxer only reads track info once). But in the case below if |it|
indicates that the track with a given id wasn't found (unlikely, but might
happen), then we should not try to access it->second (since that could lead to
invalid memory access) and instead we better crash safely via CHECK.

+  track_id_to_demux_stream_ = tracks.OnTrackIdsAssigned(track_ids);
+}
+
+const DemuxerStream* FFmpegDemuxer::GetDemuxerStreamByTrackId(
+    unsigned track_id) const {
+  const auto& it = track_id_to_demux_stream_.find(track_id);
+  CHECK(it != track_id_to_demux_stream_.end());
+  return it->second;
+}
+
 }  // namespace media