Allow muting/unmuting audio through media track API

media/base/pipeline.h

 // 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.
 
 #ifndef MEDIA_BASE_PIPELINE_H_
 #define MEDIA_BASE_PIPELINE_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"
 #include "media/base/ranges.h"
 #include "media/base/text_track.h"
 #include "media/base/video_rotation.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace media {
 
 class Demuxer;
+class DemuxerStream;
 class Renderer;
 class VideoFrame;
 
 // Metadata describing a pipeline once it has been initialized.
 struct PipelineMetadata {
   PipelineMetadata()
       : has_audio(false), has_video(false), video_rotation(VIDEO_ROTATION_0) {}
 
   bool has_audio;
   bool has_video;
@@ skipping 116 matching lines @@
 
   // Return true if loading progress has been made since the last time this
   // method was called.
   virtual bool DidLoadingProgress() = 0;
 
   // Gets the current pipeline statistics.
   virtual PipelineStatistics GetStatistics() const = 0;
 
   virtual void SetCdm(CdmContext* cdm_context,
                       const CdmAttachedCB& cdm_attached_cb) = 0;
+
+  // Notifies pipeline that the set of enabled audio streams/tracks has changed.

[wolenetz, 2016/03/30 00:31:32]

Would these be better located in PipelineController? Or DemuxerHost?

Also, |enabledAudioStreams| can be an empty vector, which means audio is
disabled, right? Please add that to comment here, like you have for the video
method.

+  virtual void OnEnabledAudioStreamsChanged(
+      const std::vector<const DemuxerStream*>& enabledAudioStreams) {}
+
+  // Notifies pipeline 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) {}
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_PIPELINE_H_