[PPAPI] Pepper MediaStream API audio track implementation and example.

content/renderer/pepper/pepper_media_stream_audio_track_host.h

+// Copyright (c) 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 CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_
+#define CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_
+
+#include "base/atomicops.h"
+#include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "content/public/renderer/media_stream_audio_sink.h"
+#include "content/renderer/pepper/pepper_media_stream_track_host_base.h"
+#include "media/audio/audio_parameters.h"
+#include "third_party/WebKit/public/platform/WebMediaStreamTrack.h"
+
+namespace base {
+class MessageLoopProxy;
+}  // namespace base
+
+namespace content {
+
+class PepperMediaStreamAudioTrackHost : public PepperMediaStreamTrackHostBase {
+ public:
+  PepperMediaStreamAudioTrackHost(RendererPpapiHost* host,
+                                  PP_Instance instance,
+                                  PP_Resource resource,
+                                  const blink::WebMediaStreamTrack& track);
+
+ private:
+  // A helper class for receiving audio samples in the audio thread.
+  class AudioSink : public MediaStreamAudioSink,
+                    public base::SupportsWeakPtr<AudioSink> {

[yzshen1, 2014/01/29 21:28:06]

Please comment about on which thread weak pointers are dereferenced /
invalidates. (You probably have read the thread-safty note in weak_ptr.h) 

[Peng, 2014/01/31 18:54:43]

Done.

[yzshen1, 2014/02/03 18:14:36]

I couldn't find the corresponding change.
On 2014/01/31 18:54:43, Peng wrote:

[Peng, 2014/02/03 19:21:08]

I added comments about the constructor and the destructor.
'This class is created and destroyed on the plugin main thread.' so the weak
pointers will be dereferenced and invalidated on the plugin main thread too,
right?

Move the comment to class level.

+   public:
+    explicit AudioSink(PepperMediaStreamAudioTrackHost* host);
+    virtual ~AudioSink();
+
+    void EnqueueFrame(int32_t index);

[yzshen1, 2014/01/29 21:28:06]

On which thread it is called?

[Peng, 2014/01/31 18:54:43]

Done.

+
+   private:
+    void InitFramesOnMainThread(uint32_t number_of_frames, uint32_t frame_size);
+
+    // MediaStreamAudioSink overrides:
+    // Those functions are called from the audio thread.
+    virtual void OnData(const int16* audio_data,
+                        int sample_rate,
+                        int number_of_channels,
+                        int number_of_frames) OVERRIDE;
+    virtual void OnSetFormat(const media::AudioParameters& params) OVERRIDE;
+
+    // Unowned host which is available during the AudioSink's lifespan.

[yzshen1, 2014/01/29 21:28:06]

Please add comment about on which thread the member variables are accessed.

[Peng, 2014/01/31 18:54:43]

I added comment for members which will be only accessed in the audio thread.

+    PepperMediaStreamAudioTrackHost* host_;
+
+    // Timestamp of the next received audio frame.
+    base::TimeDelta timestamp_;
+
+    // Duration of one audio frame.
+    base::TimeDelta frame_duration_;
+
+    media::AudioParameters audio_params_;
+
+    // The size of frame pixels in bytes.

[yzshen1, 2014/01/29 21:28:06]

audio doesn't have pixels, right?

[Peng, 2014/01/31 18:54:43]

Done.

+    uint32_t frame_data_size_;
+
+    // Free frames can be used for sending audio samples.
+    // Each bit of |frames_| represents a frame index.
+    base::subtle::Atomic32 frames_;

[yzshen1, 2014/01/29 21:28:06]

Do you mean the current implementation only supports up to 32 free frames?

[Peng, 2014/01/31 18:54:43]

Yes. I changed to Atomic64. I think it should be enough.

Currently, one audio frame is 10ms. with Atomic64, we could support up to 640ms
latency.
In my test, 1 buffer is enough for 99% cases and 3 buffers is good for all
cases.

+
+    scoped_refptr<base::MessageLoopProxy> main_message_loop_proxy_;
+
+    DISALLOW_COPY_AND_ASSIGN(AudioSink);
+  };
+
+  virtual ~PepperMediaStreamAudioTrackHost();
+
+  // PepperMediaStreamTrackHostBase overrides:
+  virtual void OnClose() OVERRIDE;
+
+  // MediaStreamFrameBuffer::Delegate overrides:
+  virtual bool OnNewFramePreEnqueued(int32_t index) OVERRIDE;
+
+  // ResourceHost overrides:
+  virtual void DidConnectPendingHostToResource() OVERRIDE;
+
+  blink::WebMediaStreamTrack track_;
+
+  // True if it has been added to |blink::WebMediaStreamTrack| as a sink.
+  bool connected_;
+
+  AudioSink audio_sink_;
+
+  DISALLOW_COPY_AND_ASSIGN(PepperMediaStreamAudioTrackHost);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_