Allow muting/unmuting audio through media track API

media/base/renderer.h

 // Copyright 2014 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.
 
 #ifndef MEDIA_BASE_RENDERER_H_
 #define MEDIA_BASE_RENDERER_H_
 
+#include <vector>
+
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
 #include "media/base/buffering_state.h"
 #include "media/base/cdm_context.h"
 #include "media/base/media_export.h"
 #include "media/base/pipeline_status.h"
 
 namespace media {
 
+class DemuxerStream;
 class DemuxerStreamProvider;
 class VideoFrame;
 
 class MEDIA_EXPORT Renderer {
  public:
   Renderer();
 
   // Stops rendering and fires any pending callbacks.
   virtual ~Renderer();
 
@@ skipping 41 matching lines @@
 
   // Returns the current media time.
   virtual base::TimeDelta GetMediaTime() = 0;
 
   // Returns whether |this| renders audio.
   virtual bool HasAudio() = 0;
 
   // Returns whether |this| renders video.
   virtual bool HasVideo() = 0;
 
+  // Notifies renderer that the set of enabled audio streams/tracks has changed.
+  // The input parameter |enabledAudioStreams| might be empty, which means that
+  // all audio tracks should be disabled/muted.
+  virtual void OnEnabledAudioStreamsChanged(
+      const std::vector<const DemuxerStream*>& enabledAudioStreams) {}

[wolenetz, 2016/04/15 23:52:17]

Is there a bug tracking getting mojo and any other users of this default
implementation to instead do "the right thing" and actuate the effect of streams
changing? If not, please file one. Either way, please reference it in TODO here
and in OnSelectedVideoStreamChanged(), below.

+
+  // Notifies renderer that the selected video stream has changed. The input
+  // parameter |selectedVideoStream| can be null, which means video is disabled.
+  virtual void OnSelectedVideoStreamChanged(
+      const DemuxerStream* selectedVideoStream) {}
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Renderer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_RENDERER_H_