[mythtv-users] Use of Macintosh G4 as MythTV box

[Greg Vickers]

Bob,

Bob wrote:
>> If you use hardware encoding capture cards (DVB-T does this, and 
>> analogue capture cards like the PVR-250) you don't need a lot of CPU 
>> for the capture of the video.
> 
> I believe the DVB cards actually don't do any encoding but neither do 
> they do any decoding, they just stream the compressed video feed they 
> pull of the air in whatever codec they receive it in (usually MPEG2), 
> but the result is the same, both the hardware encoders (Hauppauge PVR 
> cards) and the assorted digital TV cards place little demands on the 
> backend CPU.

So if I had a DVB card to receive digital free-to-air and a Hauppauge 
350 to do the (analog) cable TV signal then the 350 would do the h/w 
MPEG decoding for playback and I would probably be OK with a dual 450MHz 
host, right? :P

>> Not sure if the CPUs will be enough for playback though.  But I've 
>> played back my recordings on a P3-700 with no problems (from a remote 
>> backend).
> 
> If the G4 is to be used as a frontend as well and CPU is a problem then 
> you could output through a PVR 350 card (as long as your not planing to 
> trascode stuff to MPEG4 for storage) or an nvidia card using XvMC 
> (particularly as some of the new GPUs allegedly have MPEG4 assistance) 
> as both would assist with the decoding, but, I have *no* idea if either 
> would work in a PPC environment.

Transcoding is converting from MPEG2 to MPEG4, right? Won't the 350 
decode both MPEG2 and MPEG4 streams for playback? There's an ATI rage 
128 pro in there right now, I've got a Matrox G450 to drop in there as I 
have the cable that will adapt the Matrox video display on the second 
head to an S-video and composite display. Hmm, five minutes of tinkering 
and the system won't give me any video with the Matrox in there... fell 
at the first hurdle! I wonder if this converter cable will work with the 
ATI card ...

Can you can schedule transcoding to be done when the system is idle? 
i.e. when you are not watching 'live' TV through the system?

> I wouldn't expect it to be easy though as *all* the documents are 
> written from an i386 perspective

If it was easy we wouldn't do it, right? But thanks!

So if I had the funds available, I could go out and get a DVB card, a 
Hauppauge 350 and a video card with TV out and I'd be set with this dual 
G4 450.
Or I could get a bigger CPU system and a DVB card and some other analog 
card to capture the cable TV channel.

Oh yeah, we also have a 76 cm flat-screen CRT TV as well - will I have a 
consideration when it comes to sample rate and subsequent playback rate 
given a large TV?

Thanks,
-- 
Greg Vickers
Project Manager, IT Security
Information Technology Services
Queensland University of Technology
L12, 126 Margaret St, Brisbane

Phone: (07) 3864 9536
Email: g.vickers at qut.edu.au
IT Security web site: http://www.its.qut.edu.au/itsecurity/

CRICOS No. 00213J