Add Mac OS X synchronized audio I/O back-end

media/base/audio_bus.h

Index: media/base/audio_bus.h
===================================================================
--- media/base/audio_bus.h	(revision 157152)
+++ media/base/audio_bus.h	(working copy)
@@ -30,6 +30,11 @@
   static scoped_ptr<AudioBus> Create(int channels, int frames);
   static scoped_ptr<AudioBus> Create(const AudioParameters& params);
 
+  // Creates a new AudioBus with the given number of channels, but zero length.
+  // It's expected to be used with SetChannelData() and set_frames() to
+  // reference externally allocated memory.
+  static scoped_ptr<AudioBus> Create(int channels);

[DaleCurtis, 2012/09/17 21:17:36]

Since this technically isn't a normal Create() how about: CreateWrapper()

[Chris Rogers, 2012/09/17 22:00:42]

Ok, SGTM

+
   // Creates a new AudioBus from an existing channel vector.  Does not transfer
   // ownership of |channel_data| to AudioBus; i.e., |channel_data| must outlive
   // the returned AudioBus.  Each channel must be aligned by kChannelAlignment.
@@ -74,9 +79,11 @@
   // inf, nan, or between [-1.0, 1.0]) values in the channel data.
   float* channel(int channel) { return channel_data_[channel]; }
   const float* channel(int channel) const { return channel_data_[channel]; }
+  void SetChannelData(int channel, float* data);
 
   int channels() const { return channel_data_.size(); }
   int frames() const { return frames_; }
+  void set_frames(int frames) { frames_ = frames; }

[DaleCurtis, 2012/09/17 21:17:36]

Hmm, I was thinking more along the lines of:

void CapFrames(int frames) {
  CHECK_LE(frames, original_frames);
  frames_ = frames;
}

This would allow us to use this method inside AUAudioOutputStream, per last
week's discussions, provided we give a large initial frame size.

[Chris Rogers, 2012/09/17 22:00:42]

Hmmm, I'm pretty sure we're going to want to be able to *precisely* set the
exact number of frames.   As an aside, I think that what we're doing in
AUAudioOutputStream is a mistake, but that's another story...

 
   // Helper method for zeroing out all channels of audio data.
   void Zero();
@@ -90,6 +97,7 @@
   AudioBus(int channels, int frames);
   AudioBus(int channels, int frames, float* data);
   AudioBus(int frames, const std::vector<float*>& channel_data);
+  AudioBus(int channels);
 
   // Helper method for building |channel_data_| from a block of memory.  |data|
   // must be at least BlockSize() bytes in size.