[mythtv-users] Advice on cheap video card for low-spec mythtv box

Andy Clark mythtv at dairylogic.co.uk
Tue Jul 6 09:10:48 EDT 2004


Hi all.

Like several others, I've been building a stand-alone MythTV box based on an
EPIA motherboard (the MII-12000). The other major component in the system is
a Nebula DigiTV DVB-T card, and it's running on Fedora Core 2 with a vanilla
2.6.7 kernel patched with the -epia1 kernel patch from
http://www.epiawiki.org/. Lastly, and possibly significantly, because I'm
running Fedora Core 2 I'm not therefore running xfree86, but instead
"xorg-x11".

Pretty much everything works great except for the mpeg-2 decoding / tv-out.
Actually, in general the on-board tv-out is fine, but in attempting to get
mpeg-decoding, I've run into some issues with this (detailed below).

My investigations and attempts to get via mpeg decoding have led me to the
following conclusions :-

* mythtv / ddmpeg apparently does not work in the 2.6 kernel (my attempts
have always resulted in segfaults when using ddmpeg). It apparently can work
with a 2.4 kernel, but I understand ddmpeg is very sensitive to the version
of drm in the kernel (I haven't yet tried a 2.4 kernel myself, however).

* XvMC in mythtv does not support the via hardware. In addition, I've not
been able to get tv-out working with xvmc anyway. When applying the via /
xvmc files from http://unichrome.sf.net/ to my copy of xorg-x11 (6.7.0), I
am no longer able to use the tv-out. An identical X configuration without
the patches works, but with the patches it appears there is a vsync /
interlacing issue (two copies of the desktop displayed, one above the other,
at half the normal height). I've tried as many settings as I can think of in
XF86Config for the via driver, but I've not yet seen a stable image on my TV
after with the via xvmc patches applied.

On a more general note, I have also tried setting my video resolution
specifically to 720x576 to match the incoming mpeg stream from the DVB card,
and in the hopes of removing the requirement for video scaling by the CPU.
Unfortunately, the load is still too high in spite of this because of the
software mpeg decoding.

In any case, I'll get on the the reason for this post :). At the moment I'm
looking at one of two options - either downgrade to a 2.4 kernel and try to
get ddmpeg working, or try to find a PCI card capable of mpeg decoding and
tv-out (luckily the case I bought has space for one more card).

The former is obviously cheaper, but depending on how much the latter would
cost, I'd still be willing to pay the money for an mpeg decoder card to get
the system working in its current state and avoid the hassle of the kernel
change (but maybe I've overestimated how much work would be required to get
ddmpeg working in a 2.4 kernel).

What I was really wondering was does anyone have any experience with using
the "mpeg" feature on a radeon card? Specifically, I'm looking at the
Sapphire Radeon 7000 PCI card, which has tv-out and claims to have mpeg
"acceleration". Whether that means just scaling and colour features, or
whether it means full-blown decoding I'm not sure. The card only costs
around 25-30, and I'd be willing to pay that to get video-out working at
least until the open-source VIA support is more mature.

I've read in other mailings that there are potential issues with the tv-out
on radeon cards. However, I do already have a radeon 9800 AGP card (also
tv-out) which I'm using in a separate workstation, and while I haven't yet
got tv-out working on this system, it does mean that I have the opportunity
to ensure that I can get tv-out working on this card before I buy the other
(that's assuming that the two card will behave in the same way). Also, I'm
hoping that the fact that I'm running xorg-x11 rather than xfree86 will work
in my favour in this case, but I'll have to see.

Anyway, what would be *really* useful is if someone can confirm that they're
using a similar setup (i.e. xorg-x11 6.7.0, a radeon card and an epia m/b)
and what their experiences have been. Otherwise, any advice on specific
aspects of the setup (radeon cards in general, combined
epia/mythtv/kernel-2.6 setup, etc.) would of course be appreciated.

For what it's worth (and to avoid this request becoming an nvidia / radeon
discussion), I have read a number of the postings regarding relative
benefits of nvidia / radeon cards, and most advise that nvidia is preferred.
However, it's my understanding that nvidia cards would likely require binary
drivers to do what I want, and I'd like to avoid that if possible. Also, I
suspect the xfree86/xorg-x11 issue may add complexity. Lastly, I've actually
found somewhere which sells the above ATI card, but I've not yet seen any
cheap NVidia PCI cards with tv-out, etc. available.

Sorry for the long message. Many thanks in advance for any assistance.

Andy Clark.
-- 
"There was a lot of money in the streets, blowing along the gutters
 in the wind, and he was still surprised and amused at how many people -
 himself among them - still stopped to pick them up. And why? The books
 were free now. The /ideas/ were free. Sometimes that thought exhilarated
 him. Sometimes it frightened him" - The Stand, Stephen King

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