[mythtv-users] qam channels work with azap and mplayer but one channel stutters in mythtv.

Calin Brabandt cbrabandt at yahoo.com
Fri Sep 15 21:50:23 UTC 2006

> Using the howto from the mythtv wiki I was able to
tune all but one of my
> qam channels using Time Warner Cable here in
Greensboro, NC.  The one
> channel that doesn't work under mythtv is FOX.  The
strange thing is that
> when I tune the frequency using azap, I can watch
the channel using mplayer
> with no problems.  When the same channel plays in
mythtv, it stutters very
> badly.  Every other qam channel works without issue.



I can't offer any specific advice but I've encountered
this sort of thing myself.  Fox and ABC are 720p at
60fps.  Try changing settings, one at a time, to see
if you can obtain smooth playback.  First of all, try
changing or disabling deinterlacing.  I'm running an
Nvidia FX-5200 and XvMC so I leave deinterlacing set
to Bob.

You may need to experiment with Nvidia settings.  With
0.20, I've obtained the smoothest playback using the
'nvidia-settings' control panel to disable Video
Texture Adapter and Video Blitter Adapter "Sync to
VBlank" checkboxes (on both the "X Server XVideo
Settings" page and the OpenGL page).  
I'm running Nvidia AGP rather than Kernel AGP.  I have

Option "NVAGP" "3"

In TV Settings -> Playback, I have "OpenGL sync"
checked and "Use video as timebase" unchecked.  Your
results will likely vary.  There are many combinations
of settings.  Hopefully, you'll find settings that
work for you.

Also, on an Openchrome video system, I had problems
achieving smooth playback with audio enabled.  If I
launched the frontend with the "-v playback" option,
it was clear that frames were being dropped to
maintain A/V sync.  When I configured the audio device
in mythfrontend to any kind of nonsense (like
/dev/null or maybe just leave it blank, instead of
ALSA:default) the audio was disabled and no frames
were dropped.  Strange because I then achieved full
framerate with smooth playback.


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