media/base/audio_buffer_queue.h

   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_