media/base/audio_discard_helper.h

   1 // Copyright 2014 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_DISCARD_HELPER_H_
   6 #define MEDIA_BASE_AUDIO_DISCARD_HELPER_H_
   7
   8 #include "base/memory/ref_counted.h"
   9 #include "base/time/time.h"
  10 #include "media/base/audio_timestamp_helper.h"
  11 #include "media/base/buffers.h"
  12 #include "media/base/decoder_buffer.h"
  13 #include "media/base/media_export.h"
  14
  15 namespace media {
  16
  17 class AudioBuffer;
  18
  19 // Helper class for managing timestamps and discard events around decoding.
  20 class MEDIA_EXPORT AudioDiscardHelper {
  21  public:
  22   // |sample_rate| is the sample rate of decoded data which will be handed into
  23   // the ProcessBuffers() call.
  24   //
  25   // |decoder_delay| is the number of frames a decoder will output before data
  26   // corresponding to the first encoded buffer is output.  Callers only need to
  27   // specify this if the decoder inserts frames which have no corresponding
  28   // encoded buffer.
  29   //
  30   // For example, most MP3 decoders will output 529 junk frames before the data
  31   // corresponding to the first encoded buffer is output.  These frames are not
  32   // represented in the encoded data stream and instead are an artifact of how
  33   // most MP3 decoders work.  See http://lame.sourceforge.net/tech-FAQ.txt
  34   //
  35   // NOTE: End discard is only supported when there is no |decoder_delay|.
  36   AudioDiscardHelper(int sample_rate, size_t decoder_delay);
  37   ~AudioDiscardHelper();
  38
  39   // Converts a TimeDelta to a frame count based on the constructed sample rate.
  40   // |duration| must be positive.
  41   size_t TimeDeltaToFrames(base::TimeDelta duration) const;
  42
  43   // Resets internal state and indicates that |initial_discard| of upcoming
  44   // frames should be discarded.
  45   void Reset(size_t initial_discard);
  46
  47   // Applies discard padding from the encoded buffer along with any initial
  48   // discards.  |decoded_buffer| may be NULL, if not the timestamp and duration
  49   // will be set after discards are applied.  Returns true if |decoded_buffer|
  50   // exists after processing discard events.  Returns false if |decoded_buffer|
  51   // was NULL, is completely discarded, or a processing error occurs.
  52   //
  53   // If AudioDiscardHelper is not initialized() the timestamp of the first
  54   // |encoded_buffer| will be used as the basis for all future timestamps set on
  55   // |decoded_buffer|s.  If the first buffer has a negative timestamp it will be
  56   // clamped to zero.
  57   bool ProcessBuffers(const scoped_refptr<DecoderBuffer>& encoded_buffer,
  58                       const scoped_refptr<AudioBuffer>& decoded_buffer);
  59
  60   // Whether any buffers have been processed.
  61   bool initialized() const {
  62     return timestamp_helper_.base_timestamp() != kNoTimestamp();
  63   }
  64
  65  private:
  66   const int sample_rate_;
  67   const size_t decoder_delay_;
  68   AudioTimestampHelper timestamp_helper_;
  69
  70   size_t discard_frames_;
  71   base::TimeDelta last_input_timestamp_;
  72
  73   bool delayed_discard_;
  74   DecoderBuffer::DiscardPadding delayed_discard_padding_;
  75
  76   DISALLOW_IMPLICIT_CONSTRUCTORS(AudioDiscardHelper);
  77 };
  78
  79 }  // namespace media
  80
  81 #endif  // MEDIA_BASE_AUDIO_DISCARD_HELPER_H_