Browser-wide audio mirroring for TabCapture API

media/audio/virtual_audio_input_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_INPUT_STREAM_H_
+#define MEDIA_AUDIO_VIRTUAL_AUDIO_INPUT_STREAM_H_
+
+#include <map>
+#include <set>
+
+#include "base/cancelable_callback.h"
+#include "base/gtest_prod_util.h"
+#include "base/memory/scoped_ptr.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_manager_base.h"
+#include "media/audio/audio_parameters.h"
+#include "media/base/audio_converter.h"
+
+namespace media {
+
+class LoopbackAudioConverter;
+class VirtualAudioOutputStream;
+
+// Virtual audio input stream which is used for audio mirroring through the
+// TabCaptureApi. This audio stream uses virtual audio output streams as input

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

No need to mention TabCaptureApi, just say this is used to mix multiple audio
output streams as one input stream.

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

Done.

+// and will mix them together to render audio. It will continuously render
+// audio until the audio mirroring session is ended.
+class MEDIA_EXPORT VirtualAudioInputStream
+    : public AudioInputStream {
+ public:
+  static VirtualAudioInputStream* MakeStream(AudioManagerBase* manager,
+                                             const AudioParameters& params);
+
+  // AudioInputStream:
+  virtual bool Open() OVERRIDE;
+  virtual void Start(AudioInputCallback* callback) OVERRIDE;
+  virtual void Stop() OVERRIDE;
+  virtual void Close() OVERRIDE;
+  virtual double GetMaxVolume() OVERRIDE;
+  virtual void SetVolume(double volume) OVERRIDE;
+  virtual double GetVolume() OVERRIDE;
+  virtual void SetAutomaticGainControl(bool enabled) OVERRIDE;
+  virtual bool GetAutomaticGainControl() OVERRIDE;
+
+  // Attaches a virtual audio output stream to be used as input.
+  void AddOutputStream(

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

Mention ownership here, is VAOS owned by this class? Does this outlive VAOS? 

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

Done.
I think it's common that all streams are owned by AudioManager, so I'm not sure
it's worth mentioning that.

+      VirtualAudioOutputStream* stream, const AudioParameters& params);
+  // Detaches a virtual audio output stream that went away (i.e. video closed).

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

nit: empty line before comments. It's confusing to mention video closed here.

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

Done.

+  void RemoveOutputStream(VirtualAudioOutputStream* stream);
+
+protected:
+  friend class VirtualAudioInputStreamTest;
+  FRIEND_TEST_ALL_PREFIXES(AudioOutputControllerTest,
+                           VirtualStreamsTriggerDeviceChange);
+
+  typedef std::map<AudioParameters, LoopbackAudioConverter*> AudioConvertersMap;
+  typedef std::map<AudioOutputStream*, AudioParameters> OutputStreamParams;
+
+  void DoCallback();

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

Need more detailed comments.

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

Done.

+
+  VirtualAudioInputStream(AudioManagerBase* manager,
+                          const AudioParameters& params);
+
+  virtual ~VirtualAudioInputStream();
+
+  AudioManagerBase* audio_manager_;
+  AudioInputCallback* callback_;
+  const int buffer_duration_ms_;
+  base::Time next_read_time_;
+  scoped_array<uint8> buffer_;
+  AudioParameters params_;
+  scoped_ptr<AudioBus> audio_bus_;
+  base::CancelableClosure on_more_data_cb_;
+  // AudioConverters associated with the attached virtual audio output streams,

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

nit: empty line before comments.

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

Done.

+  // partitioned by common AudioParameters.
+  AudioConvertersMap converters_;
+  // AudioConverter that takes all the audio converters and mixes them into one

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

nit: empty line before comments.

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

Done.

+  // final audio stream.
+  AudioConverter mixer_;
+  // Maps attached output streams to their parameters. We need this later to

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

nit: empty line before comments.

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

Done.

+  // remove the virtual output stream from the right AudioConverter.
+  OutputStreamParams output_params_;
+  int num_attached_outputs_streams_;
+
+  DISALLOW_COPY_AND_ASSIGN(VirtualAudioInputStream);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_FAKE_AUDIO_INPUT_STREAM_H_