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

content/renderer/pepper/pepper_media_stream_audio_track_host.h

+// Copyright 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 <deque>
+
+#include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.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> {
+   public:
+    // This class is created and destroyed on the plugin main thread.
+    explicit AudioSink(PepperMediaStreamAudioTrackHost* host);
+    virtual ~AudioSink();
+
+    // Enqueue a free frame index into |frames_| which will be used for

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

Enqueue*s*

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

Done.

+    // sending audio samples to plugin.
+    void EnqueueFrame(int32_t index);
+
+   private:
+    void InitFramesOnMainThread(int32_t number_of_frames, int32_t frame_size);
+
+    // MediaStreamAudioSink overrides:
+    // These two functions should be called on 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.
+    PepperMediaStreamAudioTrackHost* host_;

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

This should only be accessed from the main thread, right?

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

Except for reading frame_buffer(), to get frame_size, frame_pointer, etc.

[yzshen1, 2014/02/04 18:26:13]

Please explicitly talk about it here and at the declaration of frame_buffer in
pepper_media_stream_track_host_base, explaining what is done and why it is okay.

This is something that won't be obvious for those who need to read / maintain
the code later.

[Peng, 2014/02/04 19:57:31]

Done.

+
+    // Timestamp of the next received audio frame.
+    // Access only on the audio thread.
+    base::TimeDelta timestamp_;
+
+    // Duration of one audio frame.
+    // Access only on the audio thread.
+    base::TimeDelta frame_duration_;
+
+    // Access only on the audio thread.
+    media::AudioParameters audio_params_;
+
+    // The size of a frame in bytes.
+    // Access only on the audio thread.
+    uint32_t frame_data_size_;
+
+    // A lock to protect the index queue |frames_|.
+    base::Lock lock_;
+
+    // A queue for free frame indices.
+    std::deque<int32_t> frames_;
+
+    scoped_refptr<base::MessageLoopProxy> main_message_loop_proxy_;
+
+    base::ThreadChecker capture_thread_checker_;

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

Is capture_thread == audio thread mentioned above? It seems better to make the
name consistent.

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

Done.

+
+    DISALLOW_COPY_AND_ASSIGN(AudioSink);
+  };
+
+  virtual ~PepperMediaStreamAudioTrackHost();
+
+  // PepperMediaStreamTrackHostBase overrides:
+  virtual void OnClose() OVERRIDE;
+
+  // MediaStreamFrameBuffer::Delegate overrides:
+  virtual void OnNewFrameEnqueued() OVERRIDE;
+
+  // ResourceHost overrides:
+  virtual void DidConnectPendingHostToResource() OVERRIDE;
+
+  blink::WebMediaStreamTrack track_;
+
+  // True if |audio_sink_| 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_