Increase the default buffer size from 128 to 256 on Mac

media/audio/mac/audio_manager_mac.cc

Index: media/audio/mac/audio_manager_mac.cc
diff --git a/media/audio/mac/audio_manager_mac.cc b/media/audio/mac/audio_manager_mac.cc
index b6ecf174ba9ccaae51d30b30fc13276706e6af92..b8416d291df50c5434b7c963b33397f8f39d82b4 100644
--- a/media/audio/mac/audio_manager_mac.cc
+++ b/media/audio/mac/audio_manager_mac.cc
@@ -717,17 +717,25 @@ void AudioManagerMac::HandleDeviceChanges() {
   NotifyAllOutputDeviceChangeListeners();
 }
 
-int AudioManagerMac::ChooseBufferSize(int output_sample_rate) {
-  int buffer_size = kMinimumInputOutputBufferSize;
+int AudioManagerMac::ChooseBufferSize(bool is_input, int sample_rate) {
+  // kMinimumInputOutputBufferSize is too small for the output side because
+  // CoreAudio can get into under-run if the renderer fails delivering data
+  // to the browser within the allowed time by the OS. The workaround is to
+  // use 256 samples as the default output buffer size for sample rates
+  // smaller than 96KHz.
+  // TODO(xians): Remove this workaround after WebAudio supports user defined
+  // buffer size.

[DaleCurtis, 2014/10/24 17:04:43]

Link to tracking bug?

[no longer working on chromium, 2014/10/27 10:58:51]

Done.

+  int buffer_size = is_input ?

[no longer working on chromium, 2014/10/24 10:05:29]

Dale, for the input side, we still want 128 samples as the lowest buffer size,
this is used by getUserMedia + AudioContext.createMediaStreamSource().

For the output side, this CL increase the buffer size from 128 to 256 when the
sample rates are lower than 96K, to avoid glitches.
Since most of the webrtc users use 44.1kHz or 48KHz, I don't remember we got
audio issues when the sample rate is 96KHz, so I don't increase the buffer size
for 96K.

Let me know if you have different opinion.

Thanks.

+      kMinimumInputOutputBufferSize : 2 * kMinimumInputOutputBufferSize;
   const int user_buffer_size = GetUserBufferSize();
   if (user_buffer_size) {
     buffer_size = user_buffer_size;
-  } else if (output_sample_rate > 48000) {
+  } else if (sample_rate > 48000) {
     // The default buffer size is too small for higher sample rates and may lead
     // to glitching.  Adjust upwards by multiples of the default size.
-    if (output_sample_rate <= 96000)
+    if (sample_rate <= 96000)
       buffer_size = 2 * kMinimumInputOutputBufferSize;
-    else if (output_sample_rate <= 192000)
+    else if (sample_rate <= 192000)
       buffer_size = 4 * kMinimumInputOutputBufferSize;
   }