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

[Joe Votour]

See inline.

-- Joe

--- Scott Harris <sharris at synthys.com> wrote:
> 
> > 
> > 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.

Depending on the program you use, it might have to
decode.  MPlayer supports outputting to the PVR-350
natively, but I don't think that xine and ogle do yet.

> 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.
No!  The video cards are not chained!  You would
output either to your onboard video (or whatever card
replaces it), OR to the PVR-350 card.  Not both.  Your
regular video card cannot access the PVR-350 at all. 
The "faster video card" being able to decode the data
does not help the PVR-350 at all.  Nor does the
PVR-350's MPEG-2 decoding help your regular video card
out.

Having a card that supports Xv would help out with
scaling the image, so that it is done in hardware,
instead of software.  This is not implemented in the
PVR-350 yet (and may not ever be, I don't know), but
is implemented in a fair number of recent graphics
cards.

> 
> This is a dedicated system, so no need for X at all
> really.
> 
> Thanks,
> 
> Scott
> > _______________________________________________
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> mythtv-users at mythtv.org
>
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> 


		
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