Add generic interfaces for the sinks of the media stream audio track

content/public/renderer/media_stream_audio_sink.h

+// Copyright 2013 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 CONTENT_PUBLIC_RENDERER_MEDIA_STREAM_AUDIO_SINK_H_
+#define CONTENT_PUBLIC_RENDERER_MEDIA_STREAM_AUDIO_SINK_H_
+
+#include <vector>
+
+#include "base/basictypes.h"
+#include "content/common/content_export.h"
+
+namespace blink {
+class WebMediaStreamTrack;
+}
+
+namespace media {
+class AudioParameters;
+}
+
+namespace content {
+
+class CONTENT_EXPORT MediaStreamAudioSink {
+ public:
+  // Callback on delivering the interleaved audio data.
+  // |audio_data| is the pointer to the audio data.
+  // |sample_rate| is the sample frequency of |audio_data|.
+  // |number_of_channels| is the number of audio channels of |audio_data|.
+  // |number_of_frames| is the number of audio frames in the |audio_data|.
+  virtual void OnData(const int16* audio_data,

[perkj_chrome, 2013/12/02 14:57:39]

Please document on what thread this is called on. 

[no longer working on chromium, 2013/12/03 11:45:45]

Done.

+                      int sample_rate,
+                      int number_of_channels,
+                      int number_of_frames) = 0;
+
+  // Callback called when the format of the audio stream has changed.
+  // This is called on the same thread as calling OnData().
+  virtual void OnSetFormat(const media::AudioParameters& params) = 0;

[perkj_chrome, 2013/12/02 14:57:39]

Are there no overlap between |params| and the parameters in OnData ? 
Ie, would it make more sence to have

virtual void OnData(const int16* audio_data,
                    int number_of_frames,
                    const media::AudioParameters& params) 

and remove OnSetFormat(const media::AudioParameters& params) ? 
 

[no longer working on chromium, 2013/12/03 11:45:45]

We discussed this together in our piranha plant meetings, the problem for such
approach is that the sinks need to check the format for each callback handle the
format change. And we don't want to do this.

[perkj_chrome, 2013/12/03 13:38:53]

So should sample_rate and number_of channel be removed from OnData and only
exist in AudioParams?

On 2013/12/03 11:45:45, xians1 wrote:

[no longer working on chromium, 2013/12/03 13:50:29]

No, I am afraid we can't remove them.
They are needed for the following use cases:
# webrtc (peer connection) has no callback interface for OnSetFormat, it expects
format in the data flow.
# We use sample_rate and number_of channel to check the sink clients are always
dealing the data with the right format.

+
+ protected:
+  virtual ~MediaStreamAudioSink() {}
+};
+
+CONTENT_EXPORT void AddToAudioTrack(

[perkj_chrome, 2013/12/02 14:57:39]

Document what thread this need to be called on.

[no longer working on chromium, 2013/12/03 11:45:45]

Done.

+    MediaStreamAudioSink* sink, const blink::WebMediaStreamTrack& track);
+
+CONTENT_EXPORT void RemoveFromAudioTrack(
+    MediaStreamAudioSink* sink, const blink::WebMediaStreamTrack& track);
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_RENDERER_MEDIA_STREAM_AUDIO_SINK_H_