Allow pass through buffer sizes on OSX.

media/audio/mac/audio_auhal_mac.cc

Index: media/audio/mac/audio_auhal_mac.cc
diff --git a/media/audio/mac/audio_auhal_mac.cc b/media/audio/mac/audio_auhal_mac.cc
index abbb4bfcbfa43ed531db05463163be2ac4f97cb4..0b9e62a1a9bbdf17249cd46ce0a1a341fa5d8d77 100644
--- a/media/audio/mac/audio_auhal_mac.cc
+++ b/media/audio/mac/audio_auhal_mac.cc
@@ -217,13 +217,12 @@ OSStatus AUHALStream::Render(
   TRACE_EVENT0("audio", "AUHALStream::Render");
 
   // If the stream parameters change for any reason, we need to insert a FIFO
-  // since the OnMoreData() pipeline can't handle frame size changes.  Generally
-  // this is a temporary situation which can occur after a device change has
-  // occurred but the AudioManager hasn't received the notification yet.
+  // since the OnMoreData() pipeline can't handle frame size changes.
   if (number_of_frames != number_of_frames_) {
     // Create a FIFO on the fly to handle any discrepancies in callback rates.
     if (!audio_fifo_) {
-      VLOG(1) << "Audio frame size change detected; adding FIFO to compensate.";
+      VLOG(1) << "Audio frame size changed from " << number_of_frames_ << " to "
+              << number_of_frames << "; adding FIFO to compensate.";
       audio_fifo_.reset(new AudioPullFifo(
           output_channels_,
           number_of_frames_,
@@ -509,25 +508,41 @@ bool AUHALStream::ConfigureAUHAL() {
   }
 
   // Set the buffer frame size.
-  // WARNING: Setting this value changes the frame size for all audio units in
-  // the current process.  It's imperative that the input and output frame sizes
-  // be the same as the frames_per_buffer() returned by
-  // GetDefaultOutputStreamParameters().
-  // See http://crbug.com/154352 for details.
-  UInt32 buffer_size = number_of_frames_;
-  result = AudioUnitSetProperty(
-      audio_unit_,
-      kAudioDevicePropertyBufferFrameSize,
-      kAudioUnitScope_Output,
-      0,
-      &buffer_size,
-      sizeof(buffer_size));
+  // WARNING: Setting this value changes the frame size for all input and output

[no longer working on chromium, 2014/04/17 10:25:46]

nit, it seems it is not true that this will affect the input audio units then.

[DaleCurtis, 2014/04/17 20:50:29]

Done.

+  // audio units in the current process.  As a result, the AURenderCallback must
+  // be able to handle arbitrary buffer sizes and FIFO appropriately.
+  UInt32 buffer_size = 0;
+  UInt32 property_size = sizeof(buffer_size);
+  result = AudioUnitGetProperty(audio_unit_,

[no longer working on chromium, 2014/04/16 14:57:11]

curiously, what will the value of buffer_size be when the device is opened at
the first time?

[DaleCurtis, 2014/04/16 22:56:02]

Whatever the device default is. On my MacBook Pro this is 512. If I use
Soundflower I can make the default 2048 or anything else.

+                                kAudioDevicePropertyBufferFrameSize,
+                                kAudioUnitScope_Output,
+                                0,
+                                &buffer_size,
+                                &property_size);
   if (result != noErr) {
     OSSTATUS_DLOG(ERROR, result)
-        << "AudioUnitSetProperty(kAudioDevicePropertyBufferFrameSize) failed.";
+        << "AudioUnitGetProperty(kAudioDevicePropertyBufferFrameSize) failed.";
     return false;
   }
 
+  // Only set the buffer size if we're the only active stream or the buffer size
+  // is lower than the current buffer size.
+  if (manager_->output_stream_count() == 1 || number_of_frames_ < buffer_size) {

[no longer working on chromium, 2014/04/16 14:57:11]

what happen if there are active input streams with a smaller buffer size than
|number_of_frames_|?

[DaleCurtis, 2014/04/16 22:56:02]

The "0" after kAudioUnitScope_Output controls whether this setting is for input
or output. In testing it seems sufficient to gate this setting based on output
streams for output and input for input.

This is slightly contrary to bugs in the past around input overwriting output. I
suspect that might have been related to the use of the Live path which set both
input and output values.

In any case, I'll watch for crashes around this.

[no longer working on chromium, 2014/04/17 10:25:46]

Interesting. I might be just misled by that bug.
It will be great if input and output don't need to use a same buffer size.

+    buffer_size = number_of_frames_;
+    result = AudioUnitSetProperty(audio_unit_,
+                                  kAudioDevicePropertyBufferFrameSize,
+                                  kAudioUnitScope_Output,
+                                  0,
+                                  &buffer_size,
+                                  sizeof(buffer_size));
+    if (result != noErr) {
+      OSSTATUS_DLOG(ERROR, result) << "AudioUnitSetProperty("
+                                      "kAudioDevicePropertyBufferFrameSize) "
+                                      "failed.";

[no longer working on chromium, 2014/04/16 14:57:11]

nit, including the number_of_frames_ to the log?

[DaleCurtis, 2014/04/16 22:56:02]

Done.

+      return false;
+    }
+  }
+
   // Setup callback.
   AURenderCallbackStruct callback;
   callback.inputProc = InputProc;