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;
+
+// VirtualAudioOutputStream attaches to a VirtualAudioInputStream when Start()
+// is called and is used as an audio source. VirtualAudioOutputStream also
+// implements an interface so it can be used as an input to AudioConverter so
+// that we can get audio frames that match the AudioParameters that
+// VirtualAudioInputStream expects.
+class MEDIA_EXPORT VirtualAudioOutputStream
+    : public AudioOutputStream,
+      public AudioConverter::InputCallback {
+ public:
+  static VirtualAudioOutputStream* MakeStream(AudioManagerBase* manager,
+                                              const AudioParameters& params,
+                                              VirtualAudioInputStream* target);
+
+  // 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* target);
+  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 VirtualAudioInputStream to attach to when Start() is called.
+  // This pointer should always be valid because VirtualAudioInputStream should
+  // outlive this class.
+  VirtualAudioInputStream* target_input_stream_;
+  float volume_;
+  bool attached_;
+
+  DISALLOW_COPY_AND_ASSIGN(VirtualAudioOutputStream);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_VIRTUAL_AUDIO_OUTPUT_STREAM_H_