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

[Scott Harris]

> 
> 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

Thanks for the reply, grealy appreciated.
My onboard is the following:

01:00.0 VGA compatible controller: S3 Inc. VT8375 [ProSavage8
KM266/KL266] (prog-if 00 [VGA])
        Subsystem: Micro-Star International Co., Ltd.: Unknown device
3908
        Flags: bus master, 66Mhz, medium devsel, latency 32, IRQ 11
        Memory at e5000000 (32-bit, non-prefetchable) [disabled]
[size=512K]
        Memory at d8000000 (32-bit, prefetchable) [disabled] [size=128M]
        Capabilities: [dc] Power Management version 2
        Capabilities: [80] AGP version 2.0

I think where I was confused is that I thought xine/mplayer/ogle would
need to decode the image before sending the raw data out to the pvr-350.
So, if I had a faster video card (or one that supported xv) it would be
able to decode the data faster, then just dump to the out of the 350.

This is a dedicated system, so no need for X at all really.

Thanks,

Scott