[mythtv-users] Jerky panning all cards and resolutions. Thoughts on where to look?

Daniel Kristjansson danielk at cuymedia.net
Wed Jun 13 14:01:26 UTC 2007


On Sat, 2007-05-19 at 13:26 +0100, John wrote:
> Daniel Kristjansson wrote:
> > On Mon, 2007-05-14 at 16:32 -0400, William Munson wrote:
> > It is probably your V-Sync method. Try OpenGL V-Sync and make sure you
> > disable "Sync To VBlank" in nvidia-settings for both
> > the "Video Texture Adaptor" and the "Video Blitter Adaptor"
> > under "X Server XVideo Settings". If that doesn't work try the
> > other V-Sync methods, but make sure the "Sync To VBlank"
> > settings are enabled.
> Do you mean disable or enable
> "Sync To VBlank"
Disable for OpenGL V-Sync, enable for the other methods.

FYI RTC is really the one you wan't if you can't use
OpenGL V-Sync for any reason.

> or do you only disable when you dont use OpenGL ??
You disable it whenever you are using a OpenGL V-Sync. Otherwise
MythTV will wait for the retrace using the OpenGL V-Sync, then
send the video frame to the card and the nVidia driver will make
it wait for the next retrace before it shows the frame. When
you are using RTC or another non-retrace based V-Sync method
you want the "Sync to VBlank" to be enabled, at least with the
latest drivers where this isn't a big performance hit. But if
MythTV is already using the retrace to time the showing of
frames then having "Sync to VBlank" enabled makes us wait for
two retraces for each frame, with older drivers this means we
show half as many frames as we could, leading to less than ideal
motion, and with the newer drivers it means the video is always
at least one retrace further behind audio than MythTV thinks it
is in it's A/V Sync calculation, so lip sync is less than ideal.

-- Daniel



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