[mythtv] Codec optimization (painful high motion scenes)

Ryan A. Carris rac at racarris.com
Wed Feb 5 21:05:53 EST 2003

I have this same problem, especially with Basketball games. My Athlon 
1700XP is only at ~60%, but yet I get stutters.  I was guessing it was 
something else in KDE grabbing the kernel or the harddrive.

I'm using a Nvidia on-board graphics with a VGA-->NTSC converter, so I 
doubt it is your Matrox G400.

I'm thinking about trying the Preemptive Kernel Patch or the Low Latency 
Kernel Patch.  I was reading an article yesterday (at midnight, so 
forgive me if i remember it wrong. to find it, google linux tuning) 
about the Preemptive patch.  It included a plot of an audio wave 
spectrum encoded w/ and w/o the patch.  There was clearly drops in the 
plot w/o the patch, implying that the patch did wonders.  They also said 
they could hear the difference.  The preemptive kernel patch will reduce 
the overall efficency of the proccessor but should allow the other 
processes to jump in and out of the kernel a lot quicker than normal and 
hopefully not be visually obvious.

Does anyone have experience with the Preemptive Kernel Patch?


William Preston wrote:
> I'm getting myth all tweaked out, and I'm pretty pleased with the results
> so far.  However, I'm still having painful problems with the encoding (I
> assume that's the problem) of high-motion TV (particularly big pans of the
> scene.)  That's always been the bane of video encoding codecs, so it's not
> surprising to me that a realtime encoder is having problems keeping up.
> But, has anyone managed to get it 'better'?  Most all TV is just fine
> (liveTV or recorded) for me except for what seems to be the worst (that
> I've found) for Myth--NHL hockey.  Since this involves lots of rapid,
> entire-scene pans of the rink, Myth really seems to choke on it.  I'll
> either be choppy, fuzzy/smeary, or both.
> I've tried 480X480 and up in both Mpeg (from 2500->8000 bitrate) and
> rtjpeg (quality 150->250) and neither seem up to the task.  It's
> confusing, because my CPU never seems to top out--it never really goes
> above 60%ish.  I've tried resolutions below 480X480, but they end up being
> too blurry.  I looked at the code for all the codecs living in
> /libavcodec, but it made my brain bleed.  If anyone could
> point me to what codecs to play with in there, that'd be much appreciated.
> Some video codecs allow you to optimize for 'high motion' or 'low motion',
> but myth doesn't seem to have (in the gui, at least) options to control
> this.
> (I tried setting quality min/max for mpeg4 to max=1, min=3, but my CPU was
> not up to that task.  If all I really need is a better CPU to 'fix' this,
> let me know.)
> I'm using an Athlon1600 and a WinTV-Go board, outputting with a G400
> (second head to TV--no NTSC converter).  If anyone thinks the problem is
> my G400 card (the tv-out portion) creating the problem, please let me
> know--it appears this way whether or not I have TV/out enabled, so I was
> hoping to rule that out.

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