[mythtv-users] Low End MythTV

Chris Pinkham cpinkham at bc2va.org
Tue Mar 8 00:59:55 UTC 2005


> As far as the commercial flagging taking 8hours, the machine is a
> Celeron 300, which came with the tiny 128k cache. I can only assume
> that has something to do with the slow commerical flagging time.

This probably has a HUGE impact. :)  If you figure that at 320x240,
you're frame has 76800 pixels, but at 720x480, you're up to 345600.
Commercial flagging usually only looks at the Y part of the YUV data,
so that would be 345KB per frame, which is a lot more than the amount
of data that can be cached.  1920x1088 is over 2MB, so flagging those
shows would be slow even on CPUs with larger cache.  I currently
don't scan every pixel, as the resolution gets higher, the pixel
spacing that I use for most things gets higher in order to try to
keep the speed up.  I plan on consolidating some of the methods so
that the flagging process doesn't have to scan a frame more than once,
but this is a little ways off.  Since the various detection methods
were independently created, the current code scans the frame multiple
twice (once for blank-frame detection and once for scene-change).   It
also partially scans a third time for the logo.

> (as an aside, damn commercial flagging takes a long time on HD
> content... my flag times on my main flagger went up 4x when I started
> recording HD content)

I've never profiled the code, but a huge amount of the flagging time is
spent decoding the video, so if HD content takes 4x the CPU to decode, you
could expect it to take 4x the CPU to flag. :)

-- 

Chris



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