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 {

[jochen (gone - plz use gerrit), 2013/12/02 10:24:55]

i'm not sure I understand why this interface needs to be in public/?

[no longer working on chromium, 2013/12/02 10:40:42]

This needs to be in public because chrome cast sits in chrome, and it will
implement this interface. And we only have some other implemenations like
webrtc, webaudio in content.

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

[jochen (gone - plz use gerrit), 2013/12/02 10:24:55]

why not have those as static methods MediaSreamAudioSink?

[no longer working on chromium, 2013/12/02 10:40:42]

Do you mean
#1 putting these two methods into MediaStreamAudioSink and make them static?
or #2 put them in a separate class and make them static members there?

For #1, these two methods should not belong to the MediaStreamAudioSink.
For #2, I think it is almost the same as the current approach, and I use the
current approach because it is a also used in other content/public code.

Joi, do you have any comment here? If we are going to change it to static
methods, we probably need to change the sister CL in
https://codereview.chromium.org/83023005/

[Jói, 2013/12/02 10:45:22]

This sink interface will likely be implemented by what you normally think of as
a "sink" i.e. someone receiving data from a track, but also (within content, not
outside) by the tracks themselves to receive data from a source.

If we were exposing the content::MediaStreamTrack concept to embedders, it would
make sense to have these functions as static methods of
content::MediaStreamTrack (or its audio and video specializations). But since
we're not, I think it makes most sense to have these as top-level functions.

+    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_