[mythtv] HDTV CPU utilization

Brad Templeton brad+mydev at templetons.com
Wed Jan 19 00:35:25 EST 2005

On Tue, Jan 18, 2005 at 09:33:08PM -0600, Chris Mumford wrote:
> John:
> Thanks for taking the time to reply to my questions.
> I wouldn't say plenty. I'm about 80-95% utilized so a more accurate
> description would be that I "barely" have enough CPU to do all of this in
> software. My real reason is because my system really cranks up the fans (and
> noise) when the CPU load gets above about 70%.

That is not the experience of others.  I have the same chip, Hyperthreaded
P4-3ghz, and I typically show 60% idle -- without xvmc, and sometimes
with the kernel deinterlace on not a lot less.
> > BoB deinterlacing does a VERY good job, and requires almost no extra CPU.
> I will try this once XvMC is working alright and hopefully I can leave this
> on. I don't yet have a HDTV monitor so I'm going out the S-Video connection
> of my card, which to the best of my knowledge is interlaced so I don't think
> I want deinterlacing anyhow.

Ah, not so simple, unfortunately.    BTW if you use xvmc I don't think
you get to apply any filters including deinterlace filters.  xmvc does
its own deinterlace (the name suggests to me it uses motion compensation!)

Your S-video connector puts out 480i -- 480 lines interlaced.  Your
input video is 1080i.    If you had exact scan match, you still have the
problem that 1080/480 is 2.25 -- not an integer, there are 2.25 scan lines
for each line on your screen, and since you don't have exact scan match
due to overscan etc, it's not even exactly that.

So in fact you must deinterlace your 1080i to display it nicely on your
480i screen.   Or your 480p screen.

I suppose one method would be to reduce the 1080i signal first to
960x540p, which can be done exactly, and then re-output that?  Hard
to say the best technique that would be low CPU.

Perhaps there is a way to set it so that the first 240 line sub-frame
for the 480i is drawn from the first half-frame of the 1080i, and then
repeat for the next half-frame and so on?   One presumes that would
work and take no CPU.

However, your P4-3ghz is fully capable, once you figure out your trouble,
of playing 1080i and deinterlacing it with a fancy filter.   It looks
pretty good -- better than SDTV recordings look.

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