Introduce media::AudioPushFifo and a couple of use cases (and clean-ups).

media/base/audio_rechunker.h

+// Copyright 2016 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_RECHUNKER_H_
+#define MEDIA_BASE_AUDIO_RECHUNKER_H_
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
+#include "media/base/audio_bus.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// Yet another FIFO for audio data that re-chunks audio to a desired buffer
+// size.  Unlike AudioFifo and AudioBlockFifo, this FIFO cannot overflow: The
+// client is required to provide a callback that is called synchronously during
+// a push whenever enough data becomes available.  In addition, this FIFO
+// shifts reference timestamps to account for any samples that were pending in
+// internal buffers from prior pushes.  This implementation eliminates redundant
+// memory copies when the input buffer size always matches the desired buffer
+// size.
+class MEDIA_EXPORT AudioRechunker final {
+ public:
+  using RechunkedAudioCallback =

[o1ka, 2016/02/22 13:04:47]

I think that the fact that |output| is of output_frames() size which can change
only on SetSampleRate() worth mentioning here.

+      base::Callback<void(const AudioBus& output,
+                          base::TimeDelta reference_timestamp)>;
+
+  // Creates a new AudioRechunker that re-chunks audio into the required
+  // |output_duration| and delivers it by running |callback|.
+  AudioRechunker(base::TimeDelta output_duration,
+                 const RechunkedAudioCallback& callback);
+
+  ~AudioRechunker();
+
+  int sample_rate() const { return sample_rate_; }
+
+  // Returns the number of frames in each AudioBus delivered to the
+  // RechunkedAudioCallback.
+  int output_frames() const { return output_frames_; }
+
+  // Must be called at least once before the first call to Push().  May be
+  // called later just before each audio format change.  Returns true if it is
+  // possible to EXACTLY re-chunk audio to the required |output_duration|
+  // provided to the constructor, false otherwise (e.g., 22050 Hz audio cannot
+  // be divided evenly into 10 ms chunks).
+  bool SetSampleRate(int sample_rate);

[o1ka, 2016/02/22 13:04:47]

What are the consequences of |false| return value for the clients? How they are
supposed to use it - any recommendations?

+
+  // Pushes all audio channel data from |input_bus| through the FIFO.  This will
+  // result in zero, one, or multiple synchronous calls to the
+  // RechunkedAudioCallback provided in the constructor.
+  void Push(const AudioBus& input_bus, base::TimeDelta reference_timestamp);
+
+ private:
+  const base::TimeDelta output_duration_;
+  const RechunkedAudioCallback callback_;
+
+  // These are computed in each call to SetSampleRate().
+  int sample_rate_;
+  int output_frames_;
+
+  // Queue of frames pending for delivery.
+  scoped_ptr<AudioBus> audio_queue_;
+  int pending_frames_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioRechunker);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_AUDIO_RECHUNKER_H_