Introduce AudioBus to replace std::vector<float*>.

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"
+#include "base/memory/scoped_ptr.h"
+#include "media/base/media_export.h"
+
+namespace media {
+class AudioParameters;
+
+// Scoped container for "busing" audio channel data around.

[scherkus (not reviewing), 2012/08/07 02:51:16]

I'd expand this a tiny bit more to talk about memory details -- you mention the
16-byte aligned-ness by channel() -- that seems to be pertinent information for
the class-level docs!

[DaleCurtis, 2012/08/07 18:29:45]

Done.

+class MEDIA_EXPORT AudioBus {
+ public:
+  // Creates a new AudioBus and allocates |channels| of length |frames|.  Uses
+  // channels() and frames_per_buffer() if an AudioParameters class is provided.

[scherkus (not reviewing), 2012/08/07 02:51:16]

s/class/object/

[DaleCurtis, 2012/08/07 18:29:45]

Done.

+  static scoped_ptr<AudioBus> Create(int channels, int frames);
+  static scoped_ptr<AudioBus> Create(const AudioParameters& params);
+
+  // 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.
+  static scoped_ptr<AudioBus> WrapVector(
+      int frames, const std::vector<float*>& channel_data);
+
+  // Returns a raw pointer to internal channel data.  Useful for copying state
+  // between two AudioBus object created with the same parameters.  data_size()

[scherkus (not reviewing), 2012/08/07 02:51:16]

s/object/objects/

[DaleCurtis, 2012/08/07 18:29:45]

Done.

+  // is in bytes.  Can not be used with an AudioBus constructed via wrapping.
+  void* data() const;
+  int data_size() const;
+
+  // Returns a raw pointer to the requested channel.  Pointer is guaranteed to
+  // have a 16-byte alignment.
+  float* channel(int channel) const { return channel_data_[channel]; }
+
+  int channels() const { return channel_data_.size(); }
+  int frames() const { return frames_; }
+
+  // Helper method for zeroing out all channels of audio data.
+  void ZeroFrames(int frames) const;

[scherkus (not reviewing), 2012/08/07 02:51:16]

the const attribute here is completely misleading as the data contained by this
class is getting modified

where do we need constness? if it's because of passing by const-ref I would say
don't pass by const-ref (AudioBus lives its life as a pointer, either in
scoped_ptr<T> form or T* form)

[DaleCurtis, 2012/08/07 18:29:45]

We don't for this method, I just went overboard with const'ing.  I think
supporting const ref is good since it indicates that the provided AudioBus is
merely a source.

Since the only change necessary for this is a "const float* channel(x)" method,
I think it's worth having.  As such I've added that method back from the
previous patch set.

+  void Zero() const { ZeroFrames(frames_); }

[scherkus (not reviewing), 2012/08/07 02:51:16]

nit: I'd deinline this -- it's technically not a simple getter

[DaleCurtis, 2012/08/07 18:29:45]

Done.

+
+ private:
+  friend class scoped_ptr<AudioBus>;
+  ~AudioBus();
+
+  AudioBus(int channels, int frames);
+  AudioBus(int frames, const std::vector<float*>& channel_data);
+
+  // Contiguous block of channel memory.
+  scoped_ptr_malloc<float, base::ScopedPtrAlignedFree> data_;
+  int data_size_;
+
+  // Vector of pointers to each channel's audio data.

[scherkus (not reviewing), 2012/08/07 02:51:16]

with channel_data_ I think this comment is no longer being helpful :)

[DaleCurtis, 2012/08/07 18:29:45]

Done.

+  std::vector<float*> channel_data_;
+  int frames_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioBus);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_AUDIO_BUS_H_