Implement disabling and enabling media tracks

media/base/demuxer_stream.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_DEMUXER_STREAM_H_
 #define MEDIA_BASE_DEMUXER_STREAM_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
+#include "base/time/time.h"
 #include "media/base/media_export.h"
 #include "media/base/video_rotation.h"
 
 namespace media {
 
 class AudioDecoderConfig;
 class DecoderBuffer;
 class VideoDecoderConfig;
 
 class MEDIA_EXPORT DemuxerStream {
@@ skipping 64 matching lines @@
   // A DemuxerStream that returns 'true' to this may return the 'kConfigChange'
   // status from a Read() call. In this case the client is expected to be
   // capable of taking appropriate action to handle config changes. Otherwise
   // audio_decoder_config() and video_decoder_config()'s return values are
   // guaranteed to remain constant, and the client may make optimizations based
   // on this.
   virtual bool SupportsConfigChanges() = 0;
 
   virtual VideoRotation video_rotation() = 0;
 
+  // Indicates whether a DemuxerStream is currently enabled (i.e. should be
+  // decoded and rendered) or not. When a stream is disabled the current pending
+  // read (or the next read request) reports kDisabled status. Calling Read
+  // again after that will yield a kEnabled result if the stream is later

[wolenetz, 2016/05/27 20:49:42]

nit: IIUC, s/When a stream is disabled/When a stream is set to disabled/ and
s/will yield/will eventually yield either/

+  // reenabled, or end_of_stream buffer if stream ends without being reenabled.

[wolenetz, 2016/05/27 20:49:42]

nit: How precisely is it determined that a stream ends, especially if it is
disabled? I assume you mean one of the following, but they have different
implications:
1) MediaSource.endOfStream(...) has occurred, regardless of last buffer read
position or current media playback time.
2) MediaSource.endOfStream(...) has occurred, and the last read position from
the disabled stream (from when it was enabled) was the last buffered coded
frame.
3) Or something else?

[servolk, 2016/05/27 21:23:27]

Oh, sorry this comment was out of date, I've just updated it. This CL actually
implements the approach that we discussed - when a stream is disabled it will
start returning EOS. So it becomes indistinguishable from a regular ended
stream. If a stream becomes re-enabled before playback of other remaining
streams finishes, then reading from it again will resume returning buffers from
approximately |timestamp| position.

+  virtual bool enabled() const = 0;
+  virtual void set_enabled(bool enabled, base::TimeDelta timestamp) = 0;
+
  protected:
   // Only allow concrete implementations to get deleted.
   virtual ~DemuxerStream();
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_DEMUXER_STREAM_H_