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      1 // Copyright 2013 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef MEDIA_BASE_AUDIO_BUFFER_QUEUE_H_
      6 #define MEDIA_BASE_AUDIO_BUFFER_QUEUE_H_
      7 
      8 #include <deque>
      9 
     10 #include "base/basictypes.h"
     11 #include "base/memory/scoped_ptr.h"
     12 #include "media/base/audio_buffer.h"
     13 #include "media/base/media_export.h"
     14 
     15 namespace media {
     16 
     17 class AudioBus;
     18 
     19 // A queue of AudioBuffers to support reading of arbitrary chunks of a media
     20 // data source. Audio data can be copied into an AudioBus for output. The
     21 // current position can be forwarded to anywhere in the buffered data.
     22 //
     23 // This class is not inherently thread-safe. Concurrent access must be
     24 // externally serialized.
     25 class MEDIA_EXPORT AudioBufferQueue {
     26  public:
     27   AudioBufferQueue();
     28   ~AudioBufferQueue();
     29 
     30   // Clears the buffer queue.
     31   void Clear();
     32 
     33   // Appends |buffer_in| to this queue.
     34   void Append(const scoped_refptr<AudioBuffer>& buffer_in);
     35 
     36   // Reads a maximum of |frames| frames into |dest| from the current position.
     37   // Returns the number of frames read. The current position will advance by the
     38   // amount of frames read. |dest_frame_offset| specifies a starting offset into
     39   // |dest|. On each call, the frames are converted from their source format
     40   // into the destination AudioBus.
     41   int ReadFrames(int frames, int dest_frame_offset, AudioBus* dest);
     42 
     43   // Copies up to |frames| frames from current position to |dest|. Returns
     44   // number of frames copied. Doesn't advance current position. Starts at
     45   // |source_frame_offset| from current position. |dest_frame_offset| specifies
     46   // a starting offset into |dest|. On each call, the frames are converted from
     47   // their source format into the destination AudioBus.
     48   int PeekFrames(int frames,
     49                  int source_frame_offset,
     50                  int dest_frame_offset,
     51                  AudioBus* dest);
     52 
     53   // Moves the current position forward by |frames| frames. If |frames| exceeds
     54   // frames available, the seek operation will fail.
     55   void SeekFrames(int frames);
     56 
     57   // Returns the number of frames buffered beyond the current position.
     58   int frames() const { return frames_; }
     59 
     60   // Returns the current timestamp, taking into account current offset. The
     61   // value calculated based on the timestamp of the current buffer. If timestamp
     62   // for the current buffer is set to 0, then returns value that corresponds to
     63   // the last position in a buffer that had timestamp set. kNoTimestamp() is
     64   // returned if no buffers we read from had timestamp set.
     65   base::TimeDelta current_time() const { return current_time_; }
     66 
     67  private:
     68   // Definition of the buffer queue.
     69   typedef std::deque<scoped_refptr<AudioBuffer> > BufferQueue;
     70 
     71   // An internal method shared by ReadFrames() and SeekFrames() that actually
     72   // does reading. It reads a maximum of |frames| frames into |dest|. Returns
     73   // the number of frames read. The current position will be moved forward by
     74   // the number of frames read if |advance_position| is set. If |dest| is NULL,
     75   // only the current position will advance but no data will be copied.
     76   // |source_frame_offset| can be used to skip frames before reading.
     77   // |dest_frame_offset| specifies a starting offset into |dest|.
     78   int InternalRead(int frames,
     79                    bool advance_position,
     80                    int source_frame_offset,
     81                    int dest_frame_offset,
     82                    AudioBus* dest);
     83 
     84   // Updates |current_time_| with the time that corresponds to the specified
     85   // position in the buffer.
     86   void UpdateCurrentTime(BufferQueue::iterator buffer, int offset);
     87 
     88   BufferQueue::iterator current_buffer_;
     89   BufferQueue buffers_;
     90   int current_buffer_offset_;
     91 
     92   // Number of frames available to be read in the buffer.
     93   int frames_;
     94 
     95   // Keeps track of the most recent time we've seen in case the |buffers_| is
     96   // empty when our owner asks what time it is.
     97   base::TimeDelta current_time_;
     98 
     99   DISALLOW_COPY_AND_ASSIGN(AudioBufferQueue);
    100 };
    101 
    102 }  // namespace media
    103 
    104 #endif  // MEDIA_BASE_AUDIO_BUFFER_QUEUE_H_
    105