Mailing List Archive

At 07:46 AM 6/9/2003 -0400, Simon Martin-Dye wrote:

>I am trying to build a cheap MythTV system out of my discarded computer
>components. I have a PII 450 with 384MB ram. Do you guys recommend using
>the PVR-250 since it has hardware decoding for live TV? What TV out card
>should I use - does it matter?

Since I do not use a PVR-250, I can neither recommend it or discourage you
from using it. From what others say here on the list, it works fine, but
the ivtv driver is needs is still sufficiently alpha to pose some
challenges. But read the other messages here about it and form your own
opinion.

I can tell you that a PII-450 has too little CPU power to work at all well
with any capture card that passes the encoding work on to the CPU, like the
common bttv-driver cards. (I actually tried this with a Celeron 566 and a
bttv card, just as an experiment ... I got something on the order of 20%
frame loss, even with 320x240 encoding.)

The best TV-out cards seem to be the recent nVidia cards, which qork quite
reliably with nVidia's proprietary X driver (and associated kernel module).
The one I catually use here and like is the "GeForce4 MX440-SE AGP Video
Card with TV-out".

I'm assuming that this mobo has a suitable AGP slot ... not inevitable with
so old a system. If not ... I just bought a PCI-slot nVidia card as a cheap
($US20) closeout, but I haven't tried it yet. If you do need PCI, please
post a followup, and I'll report after I get to the test (probably not for
a few days yet).

A p2-450 will not be able to DECODE a full 640x480 picture,
mine (a dual p2-450) seems to limit out abotu 592x480, for
playback the dual cpu isn't too much of an advantage, so
figure about 480x480 give or take. Recording is no problem
if you have decent disks.

Brian

On Mon, 9 Jun 2003, Simon Martin-Dye wrote:

>
> I am trying to build a cheap MythTV system out of my discarded computer components.  I have a PII 450 with 384MB ram.  Do you guys
> recommend using the PVR-250 since it has hardware decoding for live TV? What TV out card should I use - does it matter?
>
>
> __________________________________________________________________________________________________________________________________________
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Is mythtv even capable of taking advantage of dual
processor systems? You obviously need kernel smp
support, but doesn't the application also have to have
its own smp support?

Yeah ... a pII 450 with a PVR-250 ought to work fine
for recording, but you won't do very well with
playback since decoding takes a number of cycles as
well. I do recordings in mpeg4 at 640x480 with high
settings and I haven't been able to get my xbox to
play back smoothly yet. So thats a pIII 733.


--- Brian Foddy <bfoddy@visi.com> wrote:
> A p2-450 will not be able to DECODE a full 640x480
> picture,
> mine (a dual p2-450) seems to limit out abotu
> 592x480, for
> playback the dual cpu isn't too much of an
> advantage, so
> figure about 480x480 give or take. Recording is no
> problem
> if you have decent disks.
>
> Brian
>
> On Mon, 9 Jun 2003, Simon Martin-Dye wrote:
>
> >
> > I am trying to build a cheap MythTV system out of
> my discarded computer components. I have a PII 450
> with 384MB ram. Do you guys
> > recommend using the PVR-250 since it has hardware
> decoding for live TV? What TV out card should I use
> - does it matter?
> >
> >
> >
>
__________________________________________________________________________________________________________________________________________
> > Add photos to your messages with MSN 8. Get 2
> months FREE*.
> >
>
> _______________________________________________
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> mythtv-users@snowman.net
>
http://lists.snowman.net/cgi-bin/mailman/listinfo/mythtv-users


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On Tuesday 10 June 2003 03:50 pm, Allen T. Gilliland IV wrote:
> Is mythtv even capable of taking advantage of dual
> processor systems? You obviously need kernel smp
> support, but doesn't the application also have to have
> its own smp support?
>
> Yeah ... a pII 450 with a PVR-250 ought to work fine
> for recording, but you won't do very well with
> playback since decoding takes a number of cycles as
> well. I do recordings in mpeg4 at 640x480 with high
> settings and I haven't been able to get my xbox to
> play back smoothly yet. So thats a pIII 733.
>

Allen,

Its really not too bad, but could always be better.
Mythtv has several threads per recording and a
couple per playback. So even recording a single
stream, there will be some advantage to a SMP box,
ie: the video compression, audio compression,
reading from the capture card, writing to the disk
I think are all different threads (one of the
primary developers may correct me on this). But
then add a second or third capture card and now
you can realistically get 2 CPUs each compressing
a video stream at the same time (the hardest job).

What it can't do, is use 2 cpus to compress 1
video stream (other than the supporting threads
I mentioned).

And dont forget all the system overhead
of the file io, raid control, video buffers, etc.

The end result on my dual P2-450 is while the absolute best
resolution I "could" use is a single 480x480 if I
was lucky, I find it can do 2 640x240 recordings
and a playback, or 3 640x240 (1 is a pvr) without
a playback. This is of course using my quality
settings...
rtjpeg @ 200, no sound encoding, no deinterlacing
but if I just want to watch an average TV show
say the news or other simple stuff, its fine for
me. I don't try to watch fast moving sporting
events with these settings, and when I want to
watch an HDTV show like CSI, well there is no
comparison. But its all what your expectations
are.

As for me, this box was a left over from a system
upgrade I did about a year ago and only have
a couple hundred $$ plus capture cards in it.
Eventually I'll put some extra $$ together and
do a serious upgrade to either a very fast single
cpu machine or another faster dual, but from my
estimates that would still run over $1000 and
I really just can't justify that money just to
get a better picture quality right now.

As for the PVR250, the best I've been able
to decode is 592x480 with the box doing nothing
else. Clearly 450Mhz is right on the low
side for a single, but its usable.

So yes, myth will use a SMP box, if the job
is right, but you can't simply multiply the
MHz by 2 and expect twice the performance.

Brian