[mythtv-users] Processor speed question

[Richard Lee-Morlang]

On Thu, 2003-04-17 at 10:14, Andre Lewis wrote:
> I'm getting ready to build a dedicated MythTV box for my living room: a
> dual-tuner setup with one 120GB Seagate 7200 drive, and the frontend and
> backend running on a single machine. I was planning on using an Athlon XP
> CPU, maybe a 2200. So, a few questions:
>  
> 1) How much processor speed will I need to simultaineously record one
> channel and time-shift another, both at 400x480?

I've just built up a system similar to the one you have in mind. I
haven't setup a second tuner yet, however my Athlon XP 2200 seems to be
able to capture and playback RTJPEG at 720x480 with about 30-40% CPU
usage on average. I'm planning to put a second tuner in soon, and
possibly a PVR-250 in later on. According to top, the backend typically
consumes 15 - 20% of the CPU, and the frontend typically consumes 10 -
15%. I've seen the backend spike as high as 22%, and the frontend spike
as high as 20%. 

I get occasional stutters during livetv playback. I don't think I've
noticed any while playing back a recording. I suspect this might be an
issue with IRQ sharing/prioritization. I haven't had a chance to do much
tuning yet. Obviously there's lots of CPU available.

> 2) Are there any options for hardware encoding (Matrox Marvel G200, WinTV
> PVR-250)  that are ready for prime time? 

The PVR-250 isn't ready for prime time yet. Maybe soon.

> I read a lot of threads on
> hardware encoding but am not sure where things currently stand. Will
> using one of these cards lower my processor requirements,

Yes.

>  and are there
> any tradeoffs?

Flexibility of encoding code comes to mind. Cost, in some cases. Mostly
it seems like hardware encoding support would be a winning scenario
though.

Rick