Unmute Tab Audio For Desktop Share

media/audio/virtual_audio_sink.h

+// Copyright (c) 2016 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_AUDIO_VIRTUAL_AUDIO_SINK_H_
+#define MEDIA_AUDIO_VIRTUAL_AUDIO_SINK_H_
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_parameters.h"
+#include "media/base/audio_converter.h"
+#include "media/base/audio_shifter.h"
+
+namespace media {
+
+class VirtualAudioInputStream;
+
+class MEDIA_EXPORT AudioPushSink {
+ public:
+  virtual void OnData(const AudioBus* source) = 0;
+  virtual void Start() = 0;
+  virtual void Stop() = 0;
+  virtual void Close() = 0;
+};
+
+// This class is an adapter between push model and pull model for audio stream.
+// Audio provider calls OnData() to push audio data into this class.
+// Audio consumer calls ProvideInput() to pull audio data.
+class MEDIA_EXPORT VirtualAudioSink : public AudioPushSink,
+                                      public AudioConverter::InputCallback {
+ public:
+  typedef base::Callback<void(VirtualAudioSink* sink)> AfterCloseCallback;
+
+  VirtualAudioSink(AudioParameters param,
+                   VirtualAudioInputStream* target,

[miu, 2016/04/21 00:15:25]

Please document that the caller must guarantee |target| always out-lives a
VirtualAudioSink.

[qiangchen, 2016/04/28 00:00:56]

Done.

+                   AfterCloseCallback callback);
+  ~VirtualAudioSink() override;
+
+  // AudioPushSink
+  void Start() override;

[miu, 2016/04/21 00:15:25]

From what I see, you don't need these Start/Stop methods at all.  To simplify
things, I suggest you put the Start() code in the VirtualAudioSink()
constructor, and the Stop() code in Close().

[qiangchen, 2016/04/28 00:00:56]

Done.

+  void Stop() override;
+  void Close() override;
+  void OnData(const AudioBus* source) override;

[miu, 2016/04/21 00:15:25]

1. |source| should be of type const AudioBus& (not pointer) because nullptr is
not acceptable.

2. You need to pass a reference_time argument (a base::TimeTicks that indicates
when the audio was scheduled for playout).  Then, in your impl, this timing data
needs to be passed to AudioShifter.

[qiangchen, 2016/04/28 00:00:56]

Done.

+
+  // AudioConverter::InputCallback
+  double ProvideInput(AudioBus* audio_bus,
+                      base::TimeDelta buffer_delay) override;
+
+ private:
+  bool started_;
+  AudioParameters params_;
+  VirtualAudioInputStream* target_;
+  std::unique_ptr<AudioShifter> shifter_;

[miu, 2016/04/21 00:15:25]

Don't use unnecessary indirection here for the AudioShifter.  Meaning:

  AudioShifter shifter_;  (no unique_ptr)

[qiangchen, 2016/04/28 00:00:56]

Done.

+  AfterCloseCallback after_close_callback_;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_VIRTUAL_AUDIO_SINK_H_