[mythtv-users] More XvMC data points

Patrick Ouellette pat at flying-gecko.net
Fri Dec 1 18:14:33 UTC 2006

On Fri, Dec 01, 2006 at 12:07:11PM -0500, Michael Tiller wrote:
> built MythTV from SVN recently and specifically looked and it said something
> like "OpenGL Sync: Disabled" or some such thing.  That is the correct
> setting right?  (i.e. the default setting)

I was told to try turning it on and it seems to work for me.

> using the latest NVidia driver
> I've got a 440 MX using the 8776 driver.

9629 driver.  Check the AGP settings in the xorg.conf to be sure you age
really getting full speed out of the AGP.  

> and playing with the vblank settings
> By this do you mean the instructions on the Wiki that say:
> Try using the 'nvidia-settings' control panel to disable Video Texture
> >Adapter and/or Video Blitter Adapter "Sync to VBlank" checkboxes (on the "X
> >Server XVideo Settings" page)
> I've done that.

Partially, if you enable the OpenGL vblank at compile time, you get a
check box in the TV Playback setup screen too (same screen that sets
"use video as timebase" I think).

> soundcard buffer settings
> By this do you mean turn on extra audio buffering during playback? (in the
> Playback settings on the front end)

You can try it - for my system it helps to have it turned on with the
9629 video driver, but off with the 8776 driver (don't know why).

I will say XvMC output really, really, really, really sucked on my
system before 8776, and 9629 is even better.

> and dot clock in my modeline have significantly improved my XvMC output.
> I'm lost here.  I've tried adding my own modelines but it always complains
> they aren't valid, e.g.
>        ModeLine "NTSC_60i" 14.318 768 784 848 910 483 484 492 525 Interlace
>        Modeline "720x480_60" 26.72  720 736 808 896  480 481 484 497
> -HSync +Vsync
> Leads to this in Xorg.0.log:
> (WW) NVIDIA(0): No valid modes for "720x480_60"; removing.
> (WW) NVIDIA(0): No valid modes for "NTSC_60i"; removing.
> (II) NVIDIA(0): Validated modes:
> (II) NVIDIA(0):     "1024x768"
> (II) NVIDIA(0):     "720x480"

There is a modeline calculator at

Something around this should be close:

Modeline "720x480 at 60i" 12.60 720 752 792 824 480 491 494 505 interlace

The calculator should be able to come up with something that works.  The NVidia
driver restricts modelines depending on the output format and tv

option "TVStandard" "NTSC-M"
Option "TVOutFormat" "SVIDEO"

or change SVIDEO to COMPOSITE for composite out.

If you are using an external converter, you should be able to get a
wider variety of modelines to work.

DISCALIMER: I run the SVN-HEAD version of Myth, YMMV for release



Patrick Ouellette                 pat at flying-gecko.net
kb8pym at arrl.net                   Amateur Radio: KB8PYM 
Living life to a Jimmy Buffett soundtrack
"Crank the amp to 11, this needs more cowbell - and a llama wouldn't hurt either"

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