[mythtv-users] Need help picking out new motherboard / cpu

[Daniel Walton]

Just a point of reference for the cpu/decoding discussion....I'm still setting
up myth with my pcHDTV card but I've been playing around with capturing streams
with getatsc and playing them back with mplayer.  I'm on an Athlon XP 2800 with
MX440 nVIDIA video card and was trying to play back a 15 second 1080 clip of the
local news.

- prior to upgrading my video card drivers from whatever the original Fedore
Core installed, I couldn't play my captured mpg at all.  The sound was very
choppy/out of sync and the video was jerky.  The cpu was pegged :(

- upgraded the video drivers to nvidia's latest (the driver recommended in
Jarod's guide doesn't play well with kde 3.2) and things got better (less jerky,
could hear more audio) but still wasn't perfect and the cpu was still pegged.

- Edited my XFree86 setting to enable all the hardware goodies of the MX440 and
now I can play the stream with no jerks or audio problems with the cpu at 85%

So if you are going to do HD I wouldn't go any slower than an Athlon 2800.

Daniel

On Tue, 30 Mar 2004, Jarod Wilson wrote:

> On Mar 29, 2004, at 23:17, Kevin D. Snodgrass wrote:
>
> > James Armstrong wrote:
> >> I have the useless Via133 chipset and need a new backend / frontend. I
> >> was going to use my Athlon 900 for the backend and get a new frontend
> >> capable of playing HDTV until the 900 started having DMA problems. My
> >> question is, what will I need to have a combined backend/frontend
> >> capable of recording from two PVR250's and one pcHDTV card and watch
> >> at
> >
> > Note: I don't have my MythTV box built yet.  All parts are in except
> > the case/power supply. (ARRRRGH!)  But I have read about this stuff
> > for several months and had to do essentially the same evaluation you
> > are currently doing.
> >
> > The PVR-250s don't really take any CPU time, the do all the heavy
> > lifting on-board.  I don't know about the pcHDTV, but I think it has a
> > hardware compression chip built-in so it shouldn't stress the CPU much
> > either.
>
> Very little heavy lifting required for capture with the pcHDTV, but not
> because it has any hardware compression. HDTV is nothing but an
> mpeg2-transport stream, which the pcHDTV simply tunes to and writes out
> to disk. All the encoding/compression was already done at the broadcast
> end.
>
> > Watching is a different matter, but it still isn't going to stress a
> > modern CPU too much.
>
> Standard-def TV won't, but HDTV will. A common recommendation is for a
> 3GHz HT P4. I have an Athlon XP 3200 for this very reason, but haven't
> played with my pcHDTV card in ages...
>
> >> the same time? Will one of the following processors be better: P4
> >> 2.8Ghz
> >> HT with 1Meg cache, P4 3Ghz HT 512 cache, P4 3.2Ghz HT 512 cache.
> >> Those
> >
> > I think those are all overkill for 2 PVR-250s and a pcHDTV.  But
> > better too much than not enough, right?  I opted for an AMD 2800+ and
> > 512 MB RAM for my 3 PVR-250s since I expect to do commercial cutting
> > and burning to DVD on the same system.
>
> I've seen flawless playback of full-rez, high-bitrate PVR-x50 captures
> on an Athlon 800. But no, those P4 chips are about the right ballpark
> for flawless HDTV playback. I'm not certain what the difference would
> be between the 2.8 w/1MB cache and the 3.0 w/512. I don't know enough
> about the HDTV decoding process to know if more cache or more raw
> processing power is better.
>
> >> are also the order of lowest to highest price. The difference is not
> >> much, will the 1meg cache make more difference than the higher speeds?
> >> Is 200Mhz more speed worth $60? Can I have three tuners (one being
> >> HDTV)
> >
> > I don't think the extra $60 will matter.
>
> Dunno. I'm thinking the 2.8 should be fine. You can definitely have 3
> tuners though.
>
> >> and possibly record from all and watch tv too (HDTV being worse case)
> >> or
> >> will I still need a dedicated backend?
>
> I believe any of those P4 chips should be able to handle everything.
>
> > Well, you can't record on all your turners AND watch TV via one of the
> > turners (unless you are watching what one of the turners is recording)
> > all at once.  You are short one turner there.
>
> Yes, worst-case being the 250s recording, and the pcHDTV either
> recording with you watching it or viewing live TV with it, you should
> be fine. None of the recording takes much CPU, the big hit is the HDTV
> decoding.
>
> --
> Jarod C. Wilson, RHCE
>
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