Audio software mixer.

media/audio/audio_output_mixer.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.
+
+// AudioOutputMixer is a class that implements browser-side audio mixer.
+// AudioOutputMixer implements both AudioOutputDispatcher and
+// AudioSourceCallback interfaces.
+
+#ifndef MEDIA_AUDIO_AUDIO_OUTPUT_MIXER_H_
+#define MEDIA_AUDIO_AUDIO_OUTPUT_MIXER_H_
+
+#include <map>
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/synchronization/lock.h"
+#include "base/timer.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_manager.h"
+#include "media/audio/audio_output_dispatcher.h"
+#include "media/audio/audio_parameters.h"
+
+namespace media {
+
+class MEDIA_EXPORT AudioOutputMixer
+    : public AudioOutputDispatcher,
+      public AudioOutputStream::AudioSourceCallback {
+ public:
+  AudioOutputMixer(AudioManager* audio_manager,
+                   const AudioParameters& params,
+                   const base::TimeDelta& close_delay);
+
+  // AudioOutputDispatcher interface.
+  virtual bool OpenStream() OVERRIDE;
+  virtual bool StartStream(AudioOutputStream::AudioSourceCallback* callback,
+                           AudioOutputProxy* stream_proxy) OVERRIDE;
+  virtual void StopStream(AudioOutputProxy* stream_proxy) OVERRIDE;
+  virtual void StreamVolumeSet(AudioOutputProxy* stream_proxy,
+                               double volume) OVERRIDE;
+  virtual void CloseStream(AudioOutputProxy* stream_proxy) OVERRIDE;
+  virtual void Shutdown() OVERRIDE;
+
+  // AudioSourceCallback interface.
+  virtual uint32 OnMoreData(AudioOutputStream* stream,
+                            uint8* dest,
+                            uint32 max_size,
+                            AudioBuffersState buffers_state) OVERRIDE;
+  virtual void OnError(AudioOutputStream* stream, int code) OVERRIDE;
+  virtual void WaitTillDataReady() OVERRIDE;
+
+ private:
+  friend class base::RefCountedThreadSafe<AudioOutputMixer>;
+  virtual ~AudioOutputMixer();
+
+  // Called by |close_timer_|. Closes physical stream.
+  void ClosePhysicalStream();
+
+  // The |lock_| must be acquired whenever we modify |proxies_| in the audio
+  // manager thread or accessing it in the hardware audio thread. Read in the
+  // audio manager thread is safe.
+  base::Lock lock_;
+
+  // List of audio output proxies currently being played.
+  // For every proxy we store aux structure containing data necessary for
+  // mixing.
+  struct ProxyData {
+    AudioOutputStream::AudioSourceCallback* audio_source_callback;
+    double volume;
+    int pending_bytes;
+  };
+  typedef std::map<AudioOutputProxy*, ProxyData> ProxyMap;
+  ProxyMap proxies_;
+
+  // Physical stream for this mixer.
+  scoped_ptr<AudioOutputStream> physical_stream_;
+
+  // Temporary buffer used when mixing. Allocated in the constructor
+  // to avoid constant allocation/deallocation in the callback.
+  scoped_array<uint8> mixer_data_;
+
+  // Used to post delayed tasks to ourselves that we cancel inside Shutdown().
+  base::WeakPtrFactory<AudioOutputMixer> weak_this_;
+  base::DelayTimer<AudioOutputMixer> close_timer_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioOutputMixer);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_AUDIO_OUTPUT_MIXER_H_