Adds AudioFifo class to Chrome media.

media/base/audio_fifo.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_FIFO_H_
+#define MEDIA_BASE_AUDIO_FIFO_H_
+
+#include "media/base/audio_bus.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// First-in first-out container for AudioBus elements.
+// The maximum number of audio frames in the FIFO is set at construction and
+// can not be extended dynamically.  The allocated memory is utilized as a
+// ring buffer.
+class MEDIA_EXPORT AudioFifo {
+ public:
+  // Creates a new AudioFifo and allocates |channels| of length |frames|.
+  AudioFifo(int channels, int frames);
+  virtual ~AudioFifo();
+
+  // Pushes all audio channel data from |source| to the FIFO.
+  // Returns false if the allocated space is not sufficient.  Partial data is
+  // not written to the FIFO for this overflow case.
+  bool Push(const AudioBus* source);
+
+  // Consumes |destination->frames()| audio frames from the FIFO and copies
+  // them to |destination|.
+  // Returns false if it is not possible to fill up the complete |destination|.

[DaleCurtis, 2012/09/05 13:09:22]

Reword, maybe: "Returns false if there are not enough frames available to
completely fill the |destination|."

Though now that I think about it more, this is where the bool gets a bit
confusing. Since wouldn't it make more sense to return all frames available()
even if fewer than destination->frames() are available? Then return the amount
of frames filled.

Are you expecting callers to create a new AudioBus() which matches the drained
frame count every time?

Consider AudioPullFIFO, since the current behavior would mean you can't empty
this FIFO before requesting more frames. Which, depending on how you sized the
FIFO originally means you'll overflow during Push.

I think it would be nicer to return all the frames available. Even on Push(),
sending the frames available and DLOG(ERROR)'ing a message might result in less
of a glitch.

[henrika (OOO until Aug 14), 2012/09/06 09:40:06]

Modified the API.

+  // Partial data is not copied to the audio bus for this underrun case.
+  bool Consume(AudioBus* destination);
+
+  // Empties the FIFO without deallocating any memory.
+  void Clear();
+
+  // Number of actual audio bus frames in the FIFO.

[DaleCurtis, 2012/09/05 13:09:22]

Drop the "bus".

[henrika (OOO until Aug 14), 2012/09/05 15:26:32]

Done.

[DaleCurtis, 2012/09/06 11:14:13]

Looks unchanged still?

+  int frames_in_fifo() const { return frames_in_fifo_; }
+
+ private:
+  int max_frames() const { return max_frames_in_fifo_; }
+
+  // The actual FIFO is an audio bus implemented as a ring buffer.
+  scoped_ptr<AudioBus> audio_bus_;
+
+  // Maximum number of elements the FIFO can contain.
+  // This size is set by |frames| in the constructor.

[DaleCurtis, 2012/09/05 13:09:22]

s/size/value/

[henrika (OOO until Aug 14), 2012/09/05 15:26:32]

Done.

+  const int max_frames_in_fifo_;
+
+  // Number of actual elements in the FIFO.
+  int frames_in_fifo_;
+
+  // Current read position.
+  int read_pos_;
+
+  // Current write position.
+  int write_pos_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioFifo);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_AUDIO_FIFO_H_