Add new class AudioBufferQueue.

media/base/audio_buffer_queue.h

+// Copyright 2013 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_BUFFER_QUEUE_H_
+#define MEDIA_BASE_AUDIO_BUFFER_QUEUE_H_
+
+#include <deque>
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "media/base/audio_buffer.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+class AudioBus;
+
+// A queue of AudioBuffers to support reading of arbitrary chunks of a media
+// data source. Audio data can be copied into an AudioBus for output. The
+// current position can be forwarded to anywhere in the buffered data.
+//
+// This class is not inherently thread-safe. Concurrent access must be
+// externally serialized.
+class MEDIA_EXPORT AudioBufferQueue {
+ public:
+  AudioBufferQueue();
+  ~AudioBufferQueue();
+
+  // Clears the buffer queue.
+  void Clear();
+
+  // Appends |buffer_in| to this queue.
+  void Append(const scoped_refptr<AudioBuffer>& buffer_in);
+
+  // Reads a maximum of |frames| frames into |dest| from the current position.
+  // Returns the number of frames read. The current position will advance by the
+  // amount of frames read.
+  int ReadFrames(int frames, AudioBus* dest);
+
+  // Copies up to |frames| frames from current position to |dest|. Returns
+  // number of frames copied. Doesn't advance current position. Optionally
+  // starts at a |forward_offset| from current position.
+  int PeekFrames(int frames, AudioBus* dest) {

[scherkus (not reviewing), 2013/06/20 22:05:15]

how many calls to do we have for each version of PeekFrames()?

is it enough to warrant having both versions? in general we try to avoid
overloading methods

[jrummell, 2013/06/20 23:28:58]

Peek (w/offset) called from audio_renderer_algorithm.cc (to support slower
playback). Peek (w/o offset) only called from test code, so I have removed it.

+    return PeekFrames(frames, 0, dest);
+  }
+  int PeekFrames(int frames, int forward_offset, AudioBus* dest);
+
+  // Moves the current position forward by |frames| frames. If |frames| exceeds
+  // frames available, the seek operation will fail.
+  void SeekFrames(int frames);
+
+  // Returns the number of frames buffered beyond the current position.
+  int frames() const { return frames_; }
+
+  // Returns the current timestamp, taking into account current offset. The
+  // value calculated based on the timestamp of the current buffer. If timestamp
+  // for the current buffer is set to 0, then returns value that corresponds to
+  // the last position in a buffer that had timestamp set. kNoTimestamp() is
+  // returned if no buffers we read from had timestamp set.
+  base::TimeDelta current_time() const { return current_time_; }
+
+ private:
+  // Definition of the buffer queue.
+  typedef std::deque<scoped_refptr<AudioBuffer> > BufferQueue;
+
+  // An internal method shared by ReadFrames() and SeekFrames() that actually
+  // does reading. It reads a maximum of |frames| frames into |dest|. Returns
+  // the number of frames read. The current position will be moved forward by
+  // the number of frames read if |advance_position| is set. If |dest| is NULL,
+  // only the current position will advance but no data will be copied.
+  // |forward_offset| can be used to skip frames before reading.
+  int InternalRead(int frames,
+                   bool advance_position,
+                   int forward_offset,
+                   AudioBus* dest);
+
+  // Updates |current_time_| with the time that corresponds to the specified
+  // position in the buffer.
+  void UpdateCurrentTime(BufferQueue::iterator buffer, int offset);
+
+  BufferQueue::iterator current_buffer_;
+  BufferQueue buffers_;
+  int current_buffer_offset_;
+
+  // Flag to keep track of the first buffer being added.
+  bool first_buffer_;
+
+  // Number of frames available to be read in the buffer.
+  int frames_;
+
+  // Keeps track of the most recent time we've seen in case the |buffers_| is
+  // empty when our owner asks what time it is.
+  base::TimeDelta current_time_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioBufferQueue);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_AUDIO_BUFFER_QUEUE_H_