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 <vector>
+
+#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"
+
+class MEDIA_EXPORT AudioOutputMixer
+    : public AudioOutputDispatcher,
+      public AudioOutputStream::AudioSourceCallback {
+ public:
+  AudioOutputMixer(AudioManager* audio_manager,
+                   const AudioParameters& params,
+                   base::TimeDelta close_delay);
+
+  // AudioOutputDispatcher interface.
+  virtual bool StreamOpened() OVERRIDE;
+  virtual AudioOutputStream* StreamStarted(
+      AudioOutputStream::AudioSourceCallback* callback,
+      AudioOutputProxy* stream_proxy) OVERRIDE;
+  virtual void StreamStopped(AudioOutputStream* physical_stream,
+                             AudioOutputProxy* stream_proxy) OVERRIDE;
+  virtual void StreamVolumeSet(AudioOutputStream* physical_stream,
+                               double volume) OVERRIDE;
+  virtual void StreamClosed(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>;
+  ~AudioOutputMixer();

[tommi (sloooow) - chröme, 2012/04/03 13:47:51]

virtual

[enal1, 2012/04/04 18:46:55]

Done.

+
+  // 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.
+  typedef std::vector<AudioOutputProxy*> ProxyList;

[vrk (LEFT CHROMIUM), 2012/03/30 22:25:58]

Instead of a vector of AudioOutputProxies, please change this to a map of
AudioSourceCallbacks -> struct { double volume; int pending_bytes; }. (You will
need to make AudioOutputProxy extend AudioSourceCallback, as described in the
mixer.cc file.)

You should make this change because:
- You really only want to call the AudioSourceCallback methods, and have no need
for any other AudioOutputProxy method
- AudioOutputProxy never needs pending_bytes and volume itself; it gets set by
AudioOutputMixer then used by AudioOutputMixer.

[enal1, 2012/04/04 18:46:55]

AudioOutputProxy needs to store volume, as it is part of the AudioOutputStream
interface.

Moved pending_bytes to |proxies_|.

+  ProxyList 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);
+};
+
+#endif  // MEDIA_AUDIO_AUDIO_OUTPUT_MIXER_H_