[mythtv-users] xbox + xbv framerate solution

[Derek Watson]

Dennis, this may be of interest to you...

I was recently alerted to a post in the gentoox forums that was talking 
about framerate problems with mythtv in gentoox 
(http://forums.shallax.com/viewtopic.php?t=378&highlight=mythtv). The 
problem of course was the use of xbv, but someone there indicated that the 
problem is with xv and some nvidia chipsets.

The solution it turns out is to disabled double buffering using xvattr:

xvattr -a XV_DOUBLE_BUFFER -v 0

I've confirmed that this works. While watching tv at a low framerate and 
running this in another shell, the framerate instantly comes back to 25fps. 
The only problem I can see with this now is that occasional tearing in the 
picture is visible.

So the problem is very unlikely to be with xbv as such, but more likely a 
quirk with xv and the state that it thinks the encoder is in. Maybe vertical 
retrace is taking a long time (or xv thinks it is) so doesn't flip the 
buffer as often as it should. I don't know anything about xv, but maybe 
someone with experience with it could give us a starting point on addressing 
the actual problem?

Anyway, it's certainly a passable solution to the overscan problem. :-D

Derek.

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