[mythtv] Video/audio skips with new vsync code

Doug Larrick doug at ties.org
Sun Aug 22 08:48:11 EDT 2004

Zarakin wrote:
> Hi Doug,
> I tried 60 Hz (90 won't work because I'm using the TV-Out) and the end
> result was pretty much the same.

Just guessing here.  It's possible that TV-out can't delay by one 
refreshrate (~1/2 frame interval, ~1 field interval) but only by a whole 
frame (~2x refreshrate).  So the largely invisible micro-adjustments 
that are supposed to keep things in sync are failing, and once they 
accumulate far enough we have to do a big adjustment.

Try a few things:

1. If you're not using AC3 passthrough, try turning in "Use video as 
timebase."  This will adjust the audio speed rather than video.
2. Compile with OpenGL disabled.  Maybe the OpenGL timer resolution on 
TV-out is one frame rather than one field.
3. In NuppelVideoPlayer.cpp, try changing the lines (around 1300):
                         avsync_adjustment = refreshrate;
                         avsync_adjustment = -refreshrate;
to use frame_interval rather than refreshrate.

If 2 and 3 both work (independently; no need to do both), we'll have to 
measure the timer resolution to determine how much to do adjustments, 
rather than assuming we can do a 1 refresh adjustment.

Of course, if none of this fixes the problem you'll have to do some 
further debugging as I'm out of ideas.

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