media/base/audio_splicer.cc

   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 #include "media/base/audio_splicer.h"
   6
   7 #include <cstdlib>
   8
   9 #include "base/logging.h"
  10 #include "media/base/audio_buffer.h"
  11 #include "media/base/audio_decoder_config.h"
  12 #include "media/base/audio_timestamp_helper.h"
  13 #include "media/base/buffers.h"
  14
  15 namespace media {
  16
  17 // Largest gap or overlap allowed by this class. Anything
  18 // larger than this will trigger an error.
  19 // This is an arbitrary value, but the initial selection of 50ms
  20 // roughly represents the duration of 2 compressed AAC or MP3 frames.
  21 static const int kMaxTimeDeltaInMilliseconds = 50;
  22
  23 AudioSplicer::AudioSplicer(int samples_per_second)
  24     : output_timestamp_helper_(samples_per_second),
  25       min_gap_size_(2),
  26       received_end_of_stream_(false) {
  27 }
  28
  29 AudioSplicer::~AudioSplicer() {
  30 }
  31
  32 void AudioSplicer::Reset() {
  33   output_timestamp_helper_.SetBaseTimestamp(kNoTimestamp());
  34   output_buffers_.clear();
  35   received_end_of_stream_ = false;
  36 }
  37
  38 bool AudioSplicer::AddInput(const scoped_refptr<AudioBuffer>& input) {
  39   DCHECK(!received_end_of_stream_ || input->end_of_stream());
  40
  41   if (input->end_of_stream()) {
  42     output_buffers_.push_back(input);
  43     received_end_of_stream_ = true;
  44     return true;
  45   }
  46
  47   DCHECK(input->timestamp() != kNoTimestamp());
  48   DCHECK(input->duration() > base::TimeDelta());
  49   DCHECK_GT(input->frame_count(), 0);
  50
  51   if (output_timestamp_helper_.base_timestamp() == kNoTimestamp())
  52     output_timestamp_helper_.SetBaseTimestamp(input->timestamp());
  53
  54   if (output_timestamp_helper_.base_timestamp() > input->timestamp()) {
  55     DVLOG(1) << "Input timestamp is before the base timestamp.";
  56     return false;
  57   }
  58
  59   base::TimeDelta timestamp = input->timestamp();
  60   base::TimeDelta expected_timestamp = output_timestamp_helper_.GetTimestamp();
  61   base::TimeDelta delta = timestamp - expected_timestamp;
  62
  63   if (std::abs(delta.InMilliseconds()) > kMaxTimeDeltaInMilliseconds) {
  64     DVLOG(1) << "Timestamp delta too large: " << delta.InMicroseconds() << "us";
  65     return false;
  66   }
  67
  68   int frames_to_fill = 0;
  69   if (delta != base::TimeDelta())
  70     frames_to_fill = output_timestamp_helper_.GetFramesToTarget(timestamp);
  71
  72   if (frames_to_fill == 0 || std::abs(frames_to_fill) < min_gap_size_) {
  73     AddOutputBuffer(input);
  74     return true;
  75   }
  76
  77   if (frames_to_fill > 0) {
  78     DVLOG(1) << "Gap detected @ " << expected_timestamp.InMicroseconds()
  79              << " us: " << delta.InMicroseconds() << " us";
  80
  81     // Create a buffer with enough silence samples to fill the gap and
  82     // add it to the output buffer.
  83     scoped_refptr<AudioBuffer> gap = AudioBuffer::CreateEmptyBuffer(
  84         input->channel_count(),
  85         frames_to_fill,
  86         expected_timestamp,
  87         output_timestamp_helper_.GetFrameDuration(frames_to_fill));
  88     AddOutputBuffer(gap);
  89
  90     // Add the input buffer now that the gap has been filled.
  91     AddOutputBuffer(input);
  92     return true;
  93   }
  94
  95   int frames_to_skip = -frames_to_fill;
  96
  97   DVLOG(1) << "Overlap detected @ " << expected_timestamp.InMicroseconds()
  98            << " us: "  << -delta.InMicroseconds() << " us";
  99
 100   if (input->frame_count() <= frames_to_skip) {
 101     DVLOG(1) << "Dropping whole buffer";
 102     return true;
 103   }
 104
 105   // Copy the trailing samples that do not overlap samples already output
 106   // into a new buffer. Add this new buffer to the output queue.
 107   //
 108   // TODO(acolwell): Implement a cross-fade here so the transition is less
 109   // jarring.
 110   input->TrimStart(frames_to_skip);
 111   AddOutputBuffer(input);
 112   return true;
 113 }
 114
 115 bool AudioSplicer::HasNextBuffer() const {
 116   return !output_buffers_.empty();
 117 }
 118
 119 scoped_refptr<AudioBuffer> AudioSplicer::GetNextBuffer() {
 120   scoped_refptr<AudioBuffer> ret = output_buffers_.front();
 121   output_buffers_.pop_front();
 122   return ret;
 123 }
 124
 125 void AudioSplicer::AddOutputBuffer(const scoped_refptr<AudioBuffer>& buffer) {
 126   output_timestamp_helper_.AddFrames(buffer->frame_count());
 127   output_buffers_.push_back(buffer);
 128 }
 129
 130 }  // namespace media