[mythtv-users] Choppy video [no, it's not DMA :)]

Jason Tackaberry tack at auc.ca
Sun May 11 14:11:26 EDT 2003


Hi everyone.  I have a general "encoding from tv card" issue, and while
it's not exactly MythTV specific, I figure you guys are the most
qualified to help.

Details on my system can be found here:

   http://lists.snowman.net/pipermail/mythtv-dev/2003-April/008653.html

I have been running some tests on capturing video using the scrolling
marquee on CNN.  When I view this with xawtv, it is of course quite
smooth.  However any time I capture that video to a file, it becomes 
choppy.  While the text scrolls by it sticks for a fraction of a second
after about a second interval.

This does sound to me very much like an I/O issue.  For testing
purposes, and to rule out harddisk slowness, I've disabled swap and am
writing to a RAM disk.

I've tried both mythtv and mencoder with various codecs and settings. 
With mencoder, I've tried raw copy for both audio and video.  I have
also tried disabling audio in the capture to rule out A/V sync issues. 
I have tried both stock Red Hat Linux 9 kernel, as well as 2.4.20-ck6,
which has both preemptive kernel and O(1) patches.

I have tried playing back the captured video on 3 different systems, all
of which yield the same jerkiness at the same times, so based on that it
seems to me the stuttering is in the capturing, not in the playback.

Perhaps this sort of thing just demands very precise timings and it
requires a hardware solution.  Has anyone worked through this problem
and solved it?  Can anyone with a PVR-250/350 or some other capture card
with hardware encoding comment on their experiences with this sort of
test?

Thanks,
Jason.

-- 
Jason Tackaberry  ::  tack at auc.ca  :: 705-949-2301 x330 
Academic Computing Support Specialist
Information Technology Services
Algoma University College  ::  www.auc.ca




More information about the mythtv-users mailing list