Allow muting/unmuting audio through media track API

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 e9b602fa4226cfee539de7f533ae36a35f364476..a4cfde4306c75b2e3d20c1b0b430a197b1be904b 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -1205,23 +1205,27 @@ 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.
+    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);
     } 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);
     }
+    DVLOG(5) << "Associating media_track=" << media_track
+             << " with demuxer_stream=" << streams_[i];
+    track_to_stream_map_[media_track] = streams_[i];
 
     max_duration = std::max(max_duration, streams_[i]->duration());
 
@@ -1579,4 +1583,27 @@ void FFmpegDemuxer::SetLiveness(DemuxerStream::Liveness liveness) {
   }
 }
 
+void FFmpegDemuxer::OnTrackIdAssigned(unsigned track_id,
+                                      const MediaTrack* track) {
+  DVLOG(5) << "OnTrackIdAssigned track_id=" << track_id << " track=" << track;
+  if (track) {
+    DCHECK(track_id_to_track_map_.find(track_id) ==
+           track_id_to_track_map_.end());
+    track_id_to_track_map_[track_id] = track;
+  } else {
+    DCHECK(track_id_to_track_map_.find(track_id) !=
+           track_id_to_track_map_.end());
+    track_id_to_track_map_.erase(track_id);
+  }
+}
+
+const DemuxerStream* FFmpegDemuxer::GetDemuxerStreamByTrackId(
+    unsigned track_id) const {
+  const auto& it1 = track_id_to_track_map_.find(track_id);
+  CHECK(it1 != track_id_to_track_map_.end());
+  const auto& it2 = track_to_stream_map_.find(it1->second);
+  CHECK(it2 != track_to_stream_map_.end());
+  return it2->second;
+}
+
 }  // namespace media