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

media/base/audio_renderer_sink.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_BASE_AUDIO_RENDERER_SINK_H_
 #define MEDIA_BASE_AUDIO_RENDERER_SINK_H_
 
 #include <vector>
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "media/audio/audio_parameters.h"
 #include "media/base/audio_bus.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 // AudioRendererSink is an interface representing the end-point for
 // rendered audio.  An implementation is expected to
 // periodically call Render() on a callback object.
 
 class AudioRendererSink
     : public base::RefCountedThreadSafe<media::AudioRendererSink> {
  public:
   class RenderCallback {
    public:
-    // Attempts to completely fill all channels of |audio_bus|, returns actual
+    // Attempts to completely fill all channels of |dest|, returns actual
     // number of frames filled.
-    virtual int Render(AudioBus* audio_bus, int audio_delay_milliseconds) = 0;
+    virtual int Render(AudioBus* dest, int audio_delay_milliseconds) = 0;
+
+    // Synchronized audio I/O - see InitializeIO() below.
+    virtual void RenderIO(AudioBus* source,
+                          AudioBus* dest,
+                          int audio_delay_milliseconds) {}
 
     // Signals an error has occurred.
     virtual void OnRenderError() = 0;
 
    protected:
     virtual ~RenderCallback() {}
   };
 
   // Sets important information about the audio stream format.
   // It must be called before any of the other methods.
   virtual void Initialize(const AudioParameters& params,
                           RenderCallback* callback) = 0;
 
+  // InitializeIO() may be called instead of Initialize() for clients who wish
+  // to have synchronized input and output.  |input_channels| specifies the
+  // number of input channels which will be at the same sample-rate
+  // and buffer-size as the output as specified in |params|.
+  // The callback's RenderIO() method will be called instead of Render(),
+  // providing the synchronized input data at the same time as when new
+  // output data is to be rendered.
+  virtual void InitializeIO(const AudioParameters& params,
+                            int input_channels,
+                            RenderCallback* callback) {}
+
   // Starts audio playback.
   virtual void Start() = 0;
 
   // Stops audio playback.
   virtual void Stop() = 0;
 
   // Pauses playback.
   virtual void Pause(bool flush) = 0;
 
   // Resumes playback after calling Pause().
   virtual void Play() = 0;
 
   // Sets the playback volume, with range [0.0, 1.0] inclusive.
   // Returns |true| on success.
   virtual bool SetVolume(double volume) = 0;
 
  protected:
   friend class base::RefCountedThreadSafe<AudioRendererSink>;
   virtual ~AudioRendererSink() {}
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_RENDERER_SINK_H_