[mythtv-users] Video Quality

Alan Snyder ax763 at yahoo.com
Fri Mar 12 06:27:27 EST 2004


--- Jared Luxenberg <ziplux at comcast.net> wrote:
> You're able to capture at 640x480 on an Athlong
> 1GHz?  I have an Athlon XP
> 1800+ and it can barely do MPEG4 at 480x480 with no
> filters.  Are there any
> performance tweaks you did, or maybe something I'm
> doing wrong?
> 
Yes - 640x480, 2200kbps, other options default, sound
at 44.1k mp3 with quality a notch or two better than
default, no filters or special sync options.  It uses
between 50 and 60% cpu to record, and as much as 85%
for live TV but only around 15% to play a recording.  

My PII-450 remote frontend uses 30 or 40% CPU to play.
 It displays on an LCD so deinterlacing is on but no
other playback filters.

My backend is Mandrake 9.1, frontend FC1.  I update
from CVS every week or two.  

It seems to me that myth got less CPU-hungry sometime
around the 0.13 release, but this could be a
coincidence.  I didn't try to up the resolution for a
long time because I saw how much more CPU I was using
for small increases from my original 480x480.  When I
realized that square pixels were an advantage for
certain transcoding operations, I started playing with
different 4:3 ratio resolutions and was very surprised
how efficient 640x480 is.  I wonder whether the easy
scalability of certain resolutions or 640x480 being
among the "native" resolutions for the bt878 chip is a
factor.  Regardless, I'd encourage you to start at
448x336 then for each subsequent test bump the
horizontal by four clicks (16 each) and the vertical
by three clicks and see what you get.

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