Reduce jitter from uneven SincResampler buffer size requests.

media/base/multi_channel_resampler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/multi_channel_resampler.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "media/base/audio_bus.h"
 
 namespace media {
 
 MultiChannelResampler::MultiChannelResampler(int channels,
                                              double io_sample_rate_ratio,
+                                             size_t request_size,
                                              const ReadCB& read_cb)
     : last_frame_count_(0),
       read_cb_(read_cb),
       output_frames_ready_(0) {
   // Allocate each channel's resampler.
   resamplers_.reserve(channels);
   for (int i = 0; i < channels; ++i) {
-    resamplers_.push_back(new SincResampler(io_sample_rate_ratio, base::Bind(
-        &MultiChannelResampler::ProvideInput, base::Unretained(this), i)));
+    resamplers_.push_back(new SincResampler(
+        io_sample_rate_ratio, request_size, base::Bind(
+            &MultiChannelResampler::ProvideInput, base::Unretained(this), i)));
   }
 }
 
 MultiChannelResampler::~MultiChannelResampler() {}
 
-void MultiChannelResampler::Resample(AudioBus* audio_bus, int frames) {
+void MultiChannelResampler::Resample(int frames, AudioBus* audio_bus) {
   DCHECK_EQ(static_cast<size_t>(audio_bus->channels()), resamplers_.size());
 
+  // Optimize the single channel case to avoid the chunking process below.
+  if (audio_bus->channels() == 1) {
+    resamplers_[0]->Resample(frames, audio_bus->channel(0));
+    return;
+  }
+
   // We need to ensure that SincResampler only calls ProvideInput once for each
   // channel.  To ensure this, we chunk the number of requested frames into
   // SincResampler::ChunkSize() sized chunks.  SincResampler guarantees it will
   // only call ProvideInput() once when we resample this way.
   output_frames_ready_ = 0;
-  int chunk_size = resamplers_[0]->ChunkSize();
   while (output_frames_ready_ < frames) {
+    int chunk_size = resamplers_[0]->ChunkSize();
     int frames_this_time = std::min(frames - output_frames_ready_, chunk_size);
 
     // Resample each channel.
     for (size_t i = 0; i < resamplers_.size(); ++i) {
       DCHECK_EQ(chunk_size, resamplers_[i]->ChunkSize());
 
       // Depending on the sample-rate scale factor, and the internal buffering
       // used in a SincResampler kernel, this call to Resample() will only
       // sometimes call ProvideInput().  However, if it calls ProvideInput() for
       // the first channel, then it will call it for the remaining channels,
       // since they all buffer in the same way and are processing the same
       // number of frames.
       resamplers_[i]->Resample(
-          audio_bus->channel(i) + output_frames_ready_, frames_this_time);
+          frames_this_time, audio_bus->channel(i) + output_frames_ready_);
     }
 
     output_frames_ready_ += frames_this_time;
   }
 }
 
-void MultiChannelResampler::ProvideInput(int channel, float* destination,
-                                         int frames) {
+void MultiChannelResampler::ProvideInput(int channel,
+                                         int frames,
+                                         float* destination) {
   // Get the data from the multi-channel provider when the first channel asks
   // for it.  For subsequent channels, we can just dish out the channel data
   // from that (stored in |resampler_audio_bus_|).
   if (channel == 0) {
     // Allocate staging arrays on the first request and if the frame size or
     // |destination| changes (should only happen once).
     if (!resampler_audio_bus_.get() ||
         resampler_audio_bus_->frames() != frames ||
         wrapped_resampler_audio_bus_->channel(0) != destination) {
       resampler_audio_bus_ = AudioBus::Create(resamplers_.size(), frames);
@@ skipping 28 matching lines @@
   for (size_t i = 0; i < resamplers_.size(); ++i)
     resamplers_[i]->Flush();
 }
 
 void MultiChannelResampler::SetRatio(double io_sample_rate_ratio) {
   for (size_t i = 0; i < resamplers_.size(); ++i)
     resamplers_[i]->SetRatio(io_sample_rate_ratio);
 }
 
 }  // namespace media