Allow audio system to handle synchronized low-latency audio I/O

media/audio/audio_output_controller.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_AUDIO_OUTPUT_CONTROLLER_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 65 matching lines @@
     virtual void OnPlaying(AudioOutputController* controller) = 0;
     virtual void OnPaused(AudioOutputController* controller) = 0;
     virtual void OnError(AudioOutputController* controller, int error_code) = 0;
 
    protected:
     virtual ~EventHandler() {}
   };
 
   // A synchronous reader interface used by AudioOutputController for
   // synchronous reading.
+  // TODO(crogers): find a better name for this class and the Read() method
+  // now that it can handle synchronized I/O.
   class SyncReader {
    public:
     virtual ~SyncReader() {}
 
     // Notify the synchronous reader the number of bytes in the
     // AudioOutputController not yet played. This is used by SyncReader to
     // prepare more data and perform synchronization.
     virtual void UpdatePendingBytes(uint32 bytes) = 0;
 
-    // Attempt to completely fill |audio_bus|, return the actual number of
+    // Attempt to completely fill |dest|, return the actual number of
     // frames that could be read.
-    virtual int Read(AudioBus* audio_bus) = 0;
+    // |source| may optionally be provided for input data.
+    virtual int Read(AudioBus* source, AudioBus* dest) = 0;

[henrika (OOO until Aug 14), 2012/09/11 21:44:48]

You could also create two different Read methods, one with source only and one
with both source and dest. More clear perhaps?

 
     // Close this synchronous reader.
     virtual void Close() = 0;
 
     // Poll if data is ready.
     // Not reliable, as there is no guarantee that renderer is "new-style"
     // renderer that writes metadata into buffer. After several unsuccessful
     // attempts caller should assume the data is ready even if that function
     // returns false.
     virtual bool DataReady() = 0;
@@ skipping 29 matching lines @@
   //
   // It is safe to call this method more than once. Calls after the first one
   // will have no effect.
   void Close(const base::Closure& closed_task);
 
   // Sets the volume of the audio output stream.
   void SetVolume(double volume);
 
   ///////////////////////////////////////////////////////////////////////////
   // AudioSourceCallback methods.
-  virtual int OnMoreData(AudioBus* audio_bus,
+  virtual int OnMoreData(AudioBus* dest,
                          AudioBuffersState buffers_state) OVERRIDE;
+  virtual int OnMoreIOData(AudioBus* source,
+                           AudioBus* dest,
+                           AudioBuffersState buffers_state) OVERRIDE;
   virtual void OnError(AudioOutputStream* stream, int code) OVERRIDE;
   virtual void WaitTillDataReady() OVERRIDE;
 
  protected:
     // Internal state of the source.
   enum State {
     kEmpty,
     kCreated,
     kPlaying,
     kStarting,
@@ skipping 65 matching lines @@
   // shutdown and force it to wait for the most delayed task.
   // Also, if we're shutting down, we do not want to poll for more data.
   base::WeakPtrFactory<AudioOutputController> weak_this_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputController);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_