[mythtv-users] Understanding how video cards and X work together

[Nick]

On Wed, 23 Mar 2005 17:09:18 -0800, Scott Harris <sharris at synthys.com> wrote:
> I have a slower machine and a PVR-350.  I've been messing around trying to
> get the DVD playing capabilities to work without jitters etc. 
>   
> Do I understand this correctly? 
>   
> To play a DVD, X will still be involved before sending the image to the 350?
> My current on-board video card can only get me x11.  I'm wondering if a new
> card will get me xv or something better to take the burden off of my cpu,
> then it just passes it to eh 350? 
>   
> Just trying to figure out if I'm working on solving the right problem. 

It's my understanding that if you are displaying the desktop solely on
your PVR-350 (like I do)  using it's X driver supplied with ivtv
drivers, then the capabilities of only the PVR card are important.
Currently, the PVR-350 card does not have XV support, which means when
playing back video that is not the same size as the framebuffer of the
PVR (720x480 for NTSC, 720x576 for PAL) then some scaling is required.
This is where the current problem lies when trying to use mythvideo on
the PVR-350 output - it just isn't quite quick enough to do this. (at
least on my Cel 2.4 system)

When playing live TV or PVR recordings from the PVR-350, obviously
everything is the correct size, but when trying to play XVid or DivX
files via mythvideo, usually files are not 720x480 - typically 640x352
or thereabouts and this results in the stuttering you are likely to
see. I would think that DVD playback is more likely to work, as the
frame sizes should be the same as the framebuffer, resulting in
no/less jittering.

XV support for your on-board video would be useful anyway to speed
things up when you are using your regular VGA monitor etc, and will
reduce the burden on your CPU a lot. You may find that there are newer
drivers for your VGA available with XV support. If you are only going
to be using the system for mythtv, consider whether you want to use
the 350 for all output, or use it with another video card. If you are
only going to use the 350, you do not need XV support for your other
card, as X is only running on the 350. Fingers crossed, in the near
future the X driver for the PVR-350 cards will support XV and things
will speed up no end.

In the meantime, you may want to see whether there are newer drivers
for your current on-board video chipset, or obtain a newer video card
that does have TV-Out and XV support (e.g. a recent NVidia or ATI card
- NVidia GeForce cards seems to have the edge on this mailing list in
terms of ease of installation and driver support. I have found ATI's
support to be slow and incomplete so far on my Pundit-R system, but
YMMV)

Let us know what on-board chip you have, maybe an updated driver is out.

HTH,
Nick