media/base/multi_channel_resampler.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/multi_channel_resampler.h"
   6
   7 #include "base/bind.h"
   8 #include "base/bind_helpers.h"
   9 #include "base/logging.h"
  10 #include "media/base/audio_bus.h"
  11
  12 namespace media {
  13
  14 MultiChannelResampler::MultiChannelResampler(int channels,
  15                                              double io_sample_rate_ratio,
  16                                              size_t request_size,
  17                                              const ReadCB& read_cb)
  18     : read_cb_(read_cb),
  19       wrapped_resampler_audio_bus_(AudioBus::CreateWrapper(channels)),
  20       output_frames_ready_(0) {
  21   // Allocate each channel's resampler.
  22   resamplers_.reserve(channels);
  23   for (int i = 0; i < channels; ++i) {
  24     resamplers_.push_back(new SincResampler(
  25         io_sample_rate_ratio, request_size, base::Bind(
  26             &MultiChannelResampler::ProvideInput, base::Unretained(this), i)));
  27   }
  28
  29   // Setup the wrapped AudioBus for channel data.
  30   wrapped_resampler_audio_bus_->set_frames(request_size);
  31
  32   // Allocate storage for all channels except the first, which will use the
  33   // |destination| provided to ProvideInput() directly.
  34   if (channels > 1) {
  35     resampler_audio_bus_ = AudioBus::Create(channels - 1, request_size);
  36     for (int i = 0; i < resampler_audio_bus_->channels(); ++i) {
  37       wrapped_resampler_audio_bus_->SetChannelData(
  38           i + 1, resampler_audio_bus_->channel(i));
  39     }
  40   }
  41 }
  42
  43 MultiChannelResampler::~MultiChannelResampler() {}
  44
  45 void MultiChannelResampler::Resample(int frames, AudioBus* audio_bus) {
  46   DCHECK_EQ(static_cast<size_t>(audio_bus->channels()), resamplers_.size());
  47
  48   // Optimize the single channel case to avoid the chunking process below.
  49   if (audio_bus->channels() == 1) {
  50     resamplers_[0]->Resample(frames, audio_bus->channel(0));
  51     return;
  52   }
  53
  54   // We need to ensure that SincResampler only calls ProvideInput once for each
  55   // channel.  To ensure this, we chunk the number of requested frames into
  56   // SincResampler::ChunkSize() sized chunks.  SincResampler guarantees it will
  57   // only call ProvideInput() once when we resample this way.
  58   output_frames_ready_ = 0;
  59   while (output_frames_ready_ < frames) {
  60     int chunk_size = resamplers_[0]->ChunkSize();
  61     int frames_this_time = std::min(frames - output_frames_ready_, chunk_size);
  62
  63     // Resample each channel.
  64     for (size_t i = 0; i < resamplers_.size(); ++i) {
  65       DCHECK_EQ(chunk_size, resamplers_[i]->ChunkSize());
  66
  67       // Depending on the sample-rate scale factor, and the internal buffering
  68       // used in a SincResampler kernel, this call to Resample() will only
  69       // sometimes call ProvideInput().  However, if it calls ProvideInput() for
  70       // the first channel, then it will call it for the remaining channels,
  71       // since they all buffer in the same way and are processing the same
  72       // number of frames.
  73       resamplers_[i]->Resample(
  74           frames_this_time, audio_bus->channel(i) + output_frames_ready_);
  75     }
  76
  77     output_frames_ready_ += frames_this_time;
  78   }
  79 }
  80
  81 void MultiChannelResampler::ProvideInput(int channel,
  82                                          int frames,
  83                                          float* destination) {
  84   // Get the data from the multi-channel provider when the first channel asks
  85   // for it.  For subsequent channels, we can just dish out the channel data
  86   // from that (stored in |resampler_audio_bus_|).
  87   if (channel == 0) {
  88     wrapped_resampler_audio_bus_->SetChannelData(0, destination);
  89     read_cb_.Run(output_frames_ready_, wrapped_resampler_audio_bus_.get());
  90   } else {
  91     // All channels must ask for the same amount.  This should always be the
  92     // case, but let's just make sure.
  93     DCHECK_EQ(frames, wrapped_resampler_audio_bus_->frames());
  94
  95     // Copy the channel data from what we received from |read_cb_|.
  96     memcpy(destination, wrapped_resampler_audio_bus_->channel(channel),
  97            sizeof(*wrapped_resampler_audio_bus_->channel(channel)) * frames);
  98   }
  99 }
 100
 101 void MultiChannelResampler::Flush() {
 102   for (size_t i = 0; i < resamplers_.size(); ++i)
 103     resamplers_[i]->Flush();
 104 }
 105
 106 void MultiChannelResampler::SetRatio(double io_sample_rate_ratio) {
 107   for (size_t i = 0; i < resamplers_.size(); ++i)
 108     resamplers_[i]->SetRatio(io_sample_rate_ratio);
 109 }
 110
 111 }  // namespace media