Browser-wide audio mirroring for TabCapture API

media/audio/virtual_audio_input_stream.h

Index: media/audio/virtual_audio_input_stream.h
diff --git a/media/audio/virtual_audio_input_stream.h b/media/audio/virtual_audio_input_stream.h
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+// 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;
+
+// VirtualAudioInputStream converts and mixes audio from attached
+// VirtualAudioOutputStreams into a single stream. It will continuously render
+// audio until this VirtualAudioInputStream is stopped and closed.
+class MEDIA_EXPORT VirtualAudioInputStream : public AudioInputStream {
+ public:
+  static VirtualAudioInputStream* MakeStream(AudioManagerBase* manager,
+                                             const AudioParameters& params);
+
+  virtual ~VirtualAudioInputStream();
+
+  // 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 VirtualAudioOutputStream to be used as input. This
+  // VirtualAudioInputStream must outlive all attached streams, so any attached
+  // stream must be closed (which causes a detach) before
+  // VirtualAudioInputStream is destroyed.
+  virtual void AddOutputStream(VirtualAudioOutputStream* stream,
+                               const AudioParameters& output_params);
+
+  // Detaches a VirtualAudioOutputStream and removes it as input.
+  virtual void RemoveOutputStream(VirtualAudioOutputStream* stream,
+                                  const AudioParameters& output_params);
+
+ protected:
+  friend class VirtualAudioInputStreamTest;
+  FRIEND_TEST_ALL_PREFIXES(AudioOutputControllerTest,
+                           VirtualStreamsTriggerDeviceChange);
+
+  typedef std::map<AudioParameters, LoopbackAudioConverter*> AudioConvertersMap;
+
+  VirtualAudioInputStream(AudioManagerBase* manager,
+                          const AudioParameters& params);
+
+  // When Start() is called on this class, we continuously schedule this
+  // callback to render audio using any attached VirtualAudioOutputStreams until
+  // Stop() is called.
+  void ReadAudio();
+
+  // Helper method to make sure methods are called on the audio thread. This is

[DaleCurtis, 2012/12/03 19:27:28]

This is risky. You're posting tasks to the audio thread's message loop yet using
some overridden method which may have no correlation to that loop.

You could instead just use a ThreadChecker to ensure calls always happen on the
same thread as construction. Or accept a message loop in the constructor and
pass in AudioManager->GetMessageLoop() within MakeStream().

[justinlin, 2012/12/03 21:18:42]

Done.

+  // overridden by tests.
+  virtual bool CalledOnAudioThread();
+
+  AudioManagerBase* audio_manager_;
+  AudioInputCallback* callback_;
+
+  // Non-const for testing.
+  base::TimeDelta buffer_duration_ms_;
+  scoped_array<uint8> buffer_;
+  AudioParameters params_;
+  scoped_ptr<AudioBus> audio_bus_;
+  base::CancelableClosure on_more_data_cb_;
+
+  // AudioConverters associated with the attached VirtualAudioOutputStreams,
+  // partitioned by common AudioParameters.
+  AudioConvertersMap converters_;
+
+  // AudioConverter that takes all the audio converters and mixes them into one
+  // final audio stream.
+  AudioConverter mixer_;
+
+  // Number of currently attached VirtualAudioOutputStreams.
+  int num_attached_outputs_streams_;
+
+  DISALLOW_COPY_AND_ASSIGN(VirtualAudioInputStream);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_VIRTUAL_AUDIO_INPUT_STREAM_H_