[mythtv] Reasonable avsync at startup

[Doug Larrick]

Bruce Markey wrote:

> One thing it shows is a long standing problem (at least pre-0.6!)
> with the need to slew a lot at startup before audio and video
> come into sync. It would be great if you could look into this
> to help make the best possible DVR for all of us =).
> 
> It seems that audio time and video time are initially set relative
> to the system clock. However, video is almost always way ahead
> of audio by tens of frames and has to wait for audio to catch up.

 From some experimentation this morning, it appears that the issue here 
is that when audioout comes out of pause, it still has to play the 
soundcard's entire buffer (full of zeros) before it gets around to 
playing the audio we just gave it.  My soundcard has a 64k buffer, so 
for normal audio that's just over half a second.  The best fix would 
probably be to clear out this buffer when coming out of audio pause; 
alternatively video could wait until audio hits the target time until 
unpausing.

-Doug
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