[mythtv] AV-Sync problem

[David Wong]

Hi all, 

I am running 0.21 branch with VDPAU patch #r20300, on NVidia 9400 IGP with Intel Q2D E7400 2.8GHz.

When I play some of DTV channel in my living place, I got lots of following warnings: 

"Audio 686 ms behind video but already 75 video frames queued. AV-Sync might be broken. "

and some audio buffer underrun error, both video and audio are not smooth.
Video output resolution is not important too.

It only happens in 2 SD H.264 channels from same broadcaster here. 

It looks like that audio packet, in form of libavformat packet?, is very lag behind video.
It is not very surprising as the two channels are rather low bit rate. Broadcaster makes very extreme
 configuration to accommodate 1 HD and 3 SD channels in a 21Mbps carrier. 

I check into the code. It seems the playback engine only checks enough video when pre-buffering,
 and left audio buffer unchecked. Is my observation valid? Are there anyway to both ensure enough
 video and audio before playback?

Or anyway to buffer more data? I think it is better to be measured in time rather than in data size.

Regards,
David.