[mythtv] Interesting video jitter effect

Ed Wildgoose lists at wildgooses.com
Sun Nov 28 12:25:21 UTC 2004

Hi all,  I am getting some intermittent video jitter which I *think* is 
arising when the frame display point is extremely close to the video 
card frame display point.  What happens is that the video plays find for 
a long period of time, and then perhaps after 15-30 mins it will start 
to jitter a little.  Pausing briefly fixes it.  (I haven't watched for 
long enough but I think it would then stop jittering after another 10+ mins)

I have done a little work to make the audio position pointer as smooth 
as possible.  Switching to using video for timing helps a tiny bit, but 
the basic effect still happens, hence my guess as to the cause.  
Curiously mplayer doesn't seem to exhibit this issue on this machine.

I think that there is probably some tiny amount of jitter in the sleep 
code that waits for the frame display point, and perhaps when this is 
very close to the hardware display refresh moment then the tiny sleep 
jitter is directly turning into a whole frame jitter.  I'm using bob 
deinterlacer which might make this effect more visible.

I'm using RTC for the timer and whilst I could figure out why the nvidia 
frame timer isn't kicking in (does driver version 6111 work for that?) I 
think the issue is probably something that other people must be seeing?

I need to dig into the frame sync code a little more, but does anyone 
have any other thoughts on how to tackle this (anyone else seeing it..?)


Ed W

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