Reduce jitter from uneven SincResampler buffer size requests.

media/base/multi_channel_resampler.cc

Index: media/base/multi_channel_resampler.cc
diff --git a/media/base/multi_channel_resampler.cc b/media/base/multi_channel_resampler.cc
index 9aa00d88efb20d2cebf6dad4b717432f31938adf..71c62fd3d9543861d6d3ddfa2de614b18189e130 100644
--- a/media/base/multi_channel_resampler.cc
+++ b/media/base/multi_channel_resampler.cc
@@ -13,6 +13,7 @@ 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),
@@ -20,8 +21,9 @@ MultiChannelResampler::MultiChannelResampler(int channels,
   // 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)));
   }
 }
 
@@ -30,13 +32,19 @@ 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.