media/base/audio_pull_fifo.h

   1 // Copyright (c) 2012 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_PULL_FIFO_H_
   6 #define MEDIA_BASE_AUDIO_PULL_FIFO_H_
   7
   8 #include "base/callback.h"
   9 #include "media/base/media_export.h"
  10
  11 namespace media {
  12 class AudioBus;
  13
  14 // A FIFO (First In First Out) buffer to handle mismatches in buffer sizes
  15 // between a producer and consumer. The consumer will pull data from this FIFO.
  16 // If data is already available in the FIFO, it is provided to the consumer.
  17 // If insufficient data is available to satisfy the request, the FIFO will ask
  18 // the producer for more data to fulfill a request.
  19 class MEDIA_EXPORT AudioPullFifo {
  20  public:
  21   // Callback type for providing more data into the FIFO.  Expects AudioBus
  22   // to be completely filled with data upon return; zero padded if not enough
  23   // frames are available to satisfy the request.  |frame_delay| is the number
  24   // of output frames already processed and can be used to estimate delay.
  25   typedef base::Callback<void(int frame_delay, AudioBus* audio_bus)> ReadCB;
  26
  27   // Constructs an AudioPullFifo with the specified |read_cb|, which is used to
  28   // read audio data to the FIFO if data is not already available. The internal
  29   // FIFO can contain |channel| number of channels, where each channel is of
  30   // length |frames| audio frames.
  31   AudioPullFifo(int channels, int frames, const ReadCB& read_cb);
  32   virtual ~AudioPullFifo();
  33
  34   // Consumes |frames_to_consume| audio frames from the FIFO and copies
  35   // them to |destination|. If the FIFO does not have enough data, we ask
  36   // the producer to give us more data to fulfill the request using the
  37   // ReadCB implementation.
  38   void Consume(AudioBus* destination, int frames_to_consume);
  39
  40   // Empties the FIFO without deallocating any memory.
  41   void Clear();
  42
  43  private:
  44   // Attempt to fulfill the request using what is available in the FIFO.
  45   // Append new data to the |destination| starting at |write_pos|.
  46   int ReadFromFifo(AudioBus* destination, int frames_to_provide, int write_pos);
  47
  48   // Source of data to the FIFO.
  49   const ReadCB read_cb_;
  50
  51   // Temporary audio bus to hold the data from the producer.
  52   scoped_ptr<AudioBus> fifo_;
  53   int fifo_index_;
  54
  55   DISALLOW_COPY_AND_ASSIGN(AudioPullFifo);
  56 };
  57
  58 }  // namespace media
  59
  60 #endif  // MEDIA_BASE_AUDIO_PULL_FIFO_H_