Browser-wide audio mirroring for TabCapture API

media/audio/virtual_audio_output_stream.h

+// Copyright (c) 2012 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_OUTPUT_STREAM_H_
+#define MEDIA_AUDIO_VIRTUAL_AUDIO_OUTPUT_STREAM_H_
+
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_parameters.h"
+#include "media/base/audio_converter.h"
+
+namespace media {
+
+class AudioManagerBase;
+class VirtualAudioInputStream;
+
+// Audio output stream that can be used as an AudioConverter input. This class

[Alpha Left Google, 2012/11/28 01:04:47]

First mention this is connected to VirtualAudioOutputStream and then mention
AudioConverter for mixing.

[justinlin, 2012/11/28 14:30:31]

Done.

+// substitutes for a regular audio output stream which outputs to sound
+// hardware. Instead, this is used as a source of audio by a virtual audio input

[Alpha Left Google, 2012/11/28 01:04:47]

by VirtualAudioOutputStream

[justinlin, 2012/11/28 14:30:31]

Done.

+// stream.
+class MEDIA_EXPORT VirtualAudioOutputStream
+    : public AudioOutputStream,
+      public AudioConverter::InputCallback {
+ public:
+  static VirtualAudioOutputStream* MakeStream(AudioManagerBase* manager,
+                                              const AudioParameters& params,
+                                              VirtualAudioInputStream* input);
+
+  // AudioOutputStream:
+  virtual bool Open() OVERRIDE;
+  virtual void Start(AudioSourceCallback* callback) OVERRIDE;
+  virtual void Stop() OVERRIDE;
+  virtual void SetVolume(double volume) OVERRIDE;
+  virtual void GetVolume(double* volume) OVERRIDE;
+  virtual void Close() OVERRIDE;
+
+ private:
+  VirtualAudioOutputStream(AudioManagerBase* manager,
+                           const AudioParameters& params,
+                           VirtualAudioInputStream* input);
+  virtual ~VirtualAudioOutputStream();
+
+  // AudioConverter::InputCallback:
+  virtual double ProvideInput(AudioBus* audio_bus,
+      base::TimeDelta buffer_delay) OVERRIDE;
+
+  AudioManagerBase* audio_manager_;
+  AudioSourceCallback* callback_;
+  AudioParameters params_;
+  // Pointer to the virtual audio input stream this should attach to. We expect
+  // this pointer to always be valid because we always destroy all virtual audio
+  // output streams before deleting the the virtual audio input stream.
+  VirtualAudioInputStream* input_;

[Alpha Left Google, 2012/11/28 01:04:47]

This is not really input for this class but a paired input stream. Can you
rename it to attached_input_stream_?

[justinlin, 2012/11/28 14:30:31]

Changed it to target_input_stream_. "Attached" makes it sound like the input
stream attaches to the output stream, when it's the other way around. Maybe
"paired_input_stream_"? But, then it's really only "paired" when Start() is
called.

+  float volume_;
+  bool attached_;
+
+  DISALLOW_COPY_AND_ASSIGN(VirtualAudioOutputStream);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_VIRTUAL_AUDIO_OUTPUT_STREAM_H_