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) {
   DCHECK_EQ(static_cast<size_t>(audio_bus->channels()), resamplers_.size());
 
+  // Optimize the single channel case to avoid chunking.

[henrika (OOO until Aug 14), 2013/04/27 19:43:40]

"chunking"? Is that a well known term?

[DaleCurtis, 2013/04/29 22:12:31]

Refers to the code section below.  I've updated this comment to be more clear.

+  if (audio_bus->channels() == 1) {
+    resamplers_[0]->Resample(audio_bus->channel(0), frames);
+    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,
@@ skipping 50 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