Fixing audio in mac

Fixing audio in mac

TEST=media_unittests
BUG=21574
Several problems in mac audio:
1. AudioQueueEnqueueBuffer doesn't accept empty buffers. But
   we often hit buffer underrun with various reasons. In 
   order to simulate the behavior of Windows that empty
   buffer would make the callback be called after a short time,
   we write a short buffer of silence.
2. Mac audio doesn't provide pending bytes (unplayed buffer
   size in audio buffer). This is now fixed by having a
   running counter.
3. After Stop() is called, Start() will take a long time for
   the audio packet to be played. It is found that
   AudioQueueEnqueueBuffer should be called before
   AudioQueueStart otherwise we'll hit this problem of long
   delay for start.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=26510

[Alpha Left Google, 2009-09-15 01:50:58]

Taking an example of AudioQueue usage from this page:
http://developer.apple.com/mac/library/samplecode/AudioQueueTools/listing1.html

[cpu_(ooo_6.6-7.5), 2009-09-16 17:59:03]

Sorry for the delay. Looking at this now.


On 2009/09/15 01:50:58, Alpha wrote:
> Taking an example of AudioQueue usage from this page:
>
http://developer.apple.com/mac/library/samplecode/AudioQueueTools/listing1.html

[cpu_(ooo_6.6-7.5), 2009-09-16 18:06:26]

http://codereview.chromium.org/194112/diff/1/2
File media/audio/mac/audio_output_mac.cc (right):

http://codereview.chromium.org/194112/diff/1/2#newcode184
Line 184: 
Won't it be much easier we just simply don't call AudioQueueEnqueueBuffer() if
filled == 0 ?

[Alpha Left Google, 2009-09-16 18:25:34]

http://codereview.chromium.org/194112/diff/1/2
File media/audio/mac/audio_output_mac.cc (right):

http://codereview.chromium.org/194112/diff/1/2#newcode184
Line 184: 
On 2009/09/16 18:06:26, cpu wrote:
> Won't it be much easier we just simply don't call AudioQueueEnqueueBuffer() if
> filled == 0 ?
> 

AudioQueue works as a circular buffer, if we don't enqueue buffer you don't get
a callback. The output stream is a pull base model and we can't signal it to
enqueue buffer again once there's enough buffer. So doing this to simulate the
behavior of windows. In windows, if you waveOutWrite(0) you get a callback after
~2ms.

[cpu_(ooo_6.6-7.5), 2009-09-16 23:09:43]

Ok. LGTM


On 2009/09/16 18:25:34, Alpha wrote:
> http://codereview.chromium.org/194112/diff/1/2
> File media/audio/mac/audio_output_mac.cc (right):
> 
> http://codereview.chromium.org/194112/diff/1/2#newcode184
> Line 184: 
> On 2009/09/16 18:06:26, cpu wrote:
> > Won't it be much easier we just simply don't call AudioQueueEnqueueBuffer()
if
> > filled == 0 ?
> > 
> 
> AudioQueue works as a circular buffer, if we don't enqueue buffer you don't
get
> a callback. The output stream is a pull base model and we can't signal it to
> enqueue buffer again once there's enough buffer. So doing this to simulate the
> behavior of windows. In windows, if you waveOutWrite(0) you get a callback
after
> ~2ms.