Use base::Optional for selected video track.

media/filters/ffmpeg_demuxer.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/filters/ffmpeg_demuxer.h"
 
 #include <algorithm>
 #include <memory>
 #include <set>
 #include <utility>
@@ skipping 1644 matching lines @@
     }
   }
   for (const auto& stream : enabled_streams) {
     DCHECK(stream);
     DVLOG(1) << __func__ << ": enabling stream " << stream;
     stream->set_enabled(true, currTime);
   }
 }
 
 void FFmpegDemuxer::OnSelectedVideoTrackChanged(
-    const std::vector<MediaTrack::Id>& track_ids,
+    base::Optional<MediaTrack::Id> track_id,
     base::TimeDelta currTime) {
   DCHECK(task_runner_->BelongsToCurrentThread());
-  DCHECK_LE(track_ids.size(), 1u);
 
   FFmpegDemuxerStream* selected_stream = nullptr;
-  if (!track_ids.empty()) {
-    selected_stream = track_id_to_demux_stream_map_[track_ids[0]];
+  if (track_id) {
+    selected_stream = track_id_to_demux_stream_map_[*track_id];
     DCHECK(selected_stream);
     DCHECK_EQ(DemuxerStream::VIDEO, selected_stream->type());
   }
 
   // First disable all streams that need to be disabled and then enable the
   // stream that needs to be enabled (if any).
   for (const auto& stream : streams_) {
     if (stream && stream->type() == DemuxerStream::VIDEO &&
         stream.get() != selected_stream) {
       DVLOG(1) << __func__ << ": disabling stream " << stream.get();
@@ skipping 154 matching lines @@
 
 void FFmpegDemuxer::SetLiveness(DemuxerStream::Liveness liveness) {
   DCHECK(task_runner_->BelongsToCurrentThread());
   for (const auto& stream : streams_) {
     if (stream)
       stream->SetLiveness(liveness);
   }
 }
 
 }  // namespace media