Audio software mixer.

media/audio/audio_output_proxy.h

Index: media/audio/audio_output_proxy.h
===================================================================
--- media/audio/audio_output_proxy.h	(revision 130123)
+++ media/audio/audio_output_proxy.h	(working copy)
@@ -8,6 +8,7 @@
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
 #include "base/threading/non_thread_safe.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_parameters.h"
@@ -24,6 +25,7 @@
 // physical output streams.
 class MEDIA_EXPORT AudioOutputProxy
   : public AudioOutputStream,
+  public AudioOutputStream::AudioSourceCallback,
     public NON_EXPORTED_BASE(base::NonThreadSafe) {
  public:
   // Caller keeps ownership of |dispatcher|.
@@ -37,6 +39,13 @@
   virtual void GetVolume(double* volume) OVERRIDE;
   virtual void Close() 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:
   enum State {
     kCreated,
@@ -51,14 +60,16 @@
   scoped_refptr<AudioOutputDispatcher> dispatcher_;
   State state_;
 
-  // The actual audio stream. Must be set to NULL in any state other
-  // than kPlaying.
-  AudioOutputStream* physical_stream_;
-
   // Need to save volume here, so that we can restore it in case the stream
   // is stopped, and then started again.
   double volume_;
 
+  // Callback.
+  AudioSourceCallback* audio_source_callback_;
+
+  // Lock protecting |volume_| -- we can read it in the hardware audio thread.
+  base::Lock lock_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioOutputProxy);
 };