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

media/base/audio_bus.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_BUS_H_
 #define MEDIA_BASE_AUDIO_BUS_H_
 
 #include <vector>
 
 #include "base/memory/aligned_memory.h"
@@ skipping 27 matching lines @@
 
   // Creates a new AudioBus by wrapping an existing block of memory.  Block must
   // be at least CalculateMemorySize() bytes in size.  |data| must outlive the
   // returned AudioBus.  |data| must be aligned by kChannelAlignment.
   static scoped_ptr<AudioBus> WrapMemory(int channels, int frames, void* data);
   static scoped_ptr<AudioBus> WrapMemory(const AudioParameters& params,
                                          void* data);
   // Returns the required memory size to use the WrapMemory() method.
   static int CalculateMemorySize(const AudioParameters& params);
 
+  // Calculates the required size for an AudioBus with the given params, sets
+  // |aligned_frames| to the actual frame length of each channel array.
+  static int CalculateMemorySizeFromChannels(int channels, int frames,
+                                             int* aligned_frames);

[DaleCurtis, 2012/09/11 09:44:39]

I'd prefer this to be just CalculateMemorySize(int,int) and paired with the
method above both to keep style with the existing Create(int, int),
WrapMemory(int, int) methods and because FromChannels is only half the equation.
The (int, int) method be ordered first.

Per the style guide, overloading is fine "only if a reader looking at a call
site can get a good idea of what is happening without having to first figure out
exactly which overload is being called." Which fits the bill here. 

The aligned_frames value also shouldn't be exposed as we're leaking internal
details about the AudioBus. I don't see where you're using this value so lets
not expose it.

[scherkus (not reviewing), 2012/09/11 12:13:00]

Perhaps we need an internal impl w/ |aligned_frames| to remain inside the .cc as
a static method and expose a version here that doesn't return |aligned_frames|

[DaleCurtis, 2012/09/11 12:22:23]

Yes, that's what I was thinking. 

+
   // Helper methods for converting an AudioBus from and to interleaved integer
   // data.  Expects interleaving to be [ch0, ch1, ..., chN, ch0, ch1, ...] with
   // |bytes_per_sample| per value.  Values are scaled and bias corrected during
   // conversion.  ToInterleaved() will also clip values to format range.
   // Handles uint8, int16, and int32 currently.  FromInterleaved() will zero out
   // any unfilled frames when |frames| is less than frames().
   void FromInterleaved(const void* source, int frames, int bytes_per_sample);
   void ToInterleaved(int frames, int bytes_per_sample, void* dest) const;
 
   // Similar to FromInterleaved() above, but meant for streaming sources.  Does
@@ skipping 38 matching lines @@
 
   std::vector<float*> channel_data_;
   int frames_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioBus);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_BUS_H_