[mythtv-users] Very slight jitter on high power machine

Doug Larrick doug at ties.org
Tue Dec 14 01:22:04 UTC 2004

Brad Templeton wrote:
> I finally got things working at 1080i on my HDTV.  Unfortunately, there
> is a slight, but annoying jitter.  I've read a number of the articles
> on jitter but I don't seem to have the causes of that.

>     System is fast -- DMA definitely on.  Frontend: 3ghz Pentium 4,
>     100mbit network, disks easily capable of 30 megabytes/second read on
>     the backend where video is stored.     Backend is Athlon XP 3000.
>     Idle times are good -- 50 to 60% idle time on the P4 when playing
>     the HDTV video.   Not a shortage of CPU.


> 	I am running at a native 1920 x 1080 resolution, but I have to
> 	tell Myth to use only about 1872 wide due to overscan, so xv is
> 	scaling the horizontal just a touch.  I don't think I want it to
> 	scale the vertical due to interlace issues.
>     No fancy filters or de-interlace set.  Though it seems I have the
> 	CPU for them.

This sounds quite similar to my setup.  I'd say you're almost there.  If 
it's any consolation... I ran into similar (if not worse) jitter 
issues... the difference being that I wrote code to fix them!

I would suggest running 1920x540p for video output, and turn on bob 
deinterlacing.  You will need to run the GUI at 960x540 for your sanity 
(otherwise the text is unreadable).  This is the electrical equivalent 
to your HDTV of running at 1080i, but allows you to do scaling of the 
frame (for overscan or for the zoom modes).

As far as your occasional jitter, I'd suggest making sure OpenGL vsync 
is being used (with 'mythfrontend --verbose playback), and make sure 
you're installing mythfrontend as SUID root.

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