[mythtv-users] Slowest processor for software HDTV decoding

[Brad Templeton]

On Wed, Apr 27, 2005 at 05:45:41PM -0700, Joe Barnhart wrote:
> 
> --- Seth Heckard <seth.lists at gmail.com> wrote:
> 
> > Basically, I am asking for the slowest (and theroretically cheapest)
> > processor that can decode all HD formats, and ideally have headroom
> > left over for things like commercial flagging and deinterlacing if
> > required.
> 
> I think you also have to specify the final output size.  I get the
> impression that 1280x720p output is easier than 1920x1080i.  Note, the
> SOURCE material could be in either format, but the size of the DISPLAY
> resolution is what I'm talking about here (i.e. the "modeline" you're
> using).

Actually, the final output size is not too important.  it's the size
of the HD recording that matters (either 1920x1080 or 1280x720).

Your screen might run at a different size (mine I run at 1280x720 because
that is the native resolution of the DLP in it.)   The downscale from
1080i to that size is done in hardware by xvideo, and does not affect
the CPU.

So if you you want to play HDTV, your choices are to get enough CPU
to play both (or, in the extreme, downrez all the 1080i down to 720
lines, which will take a long time if your CPU can only do 720.)


However, you don't want the slowest CPU that can do the job.  If you
max out your CPU, you will regret it, because anything else using CPU
on the system will make your video skip.   Even the fastest systems
get (rare) video skips from time to time when something fires up on
them that eats CPU, even when niced like a commercial flag.  The issue,
once you hit the minimum, is how resiliant you want it to be.

> I use a 1080i modeline and I could not use an Athlon XP 2800 and get
> satisfactory output.  I had to go to a 3GHz P4 with hyperthreading to
> get the headroom you speak of.  (Recently I discovered that 512M wasn't
> enough, either. I have two HD-3000 cards, and comm flagging was killing
> me at 512M.)

Some people are reporting ok playback on systems like a 2.4ghz.  I
recommend spending a few extra bucks and going higher.   Some claim to
have gone even lower, at least for 720p.

Of course, if you use xvmc, you can get by with much less.  Note that
xvmc can't help you with mp4 at this time, if you do plan to transcode.