[mythtv-users] Bob deinterlace and Xv problems

Tom Lichti tom at redpepperracing.com
Fri May 12 10:32:15 EDT 2006

Doug Larrick wrote:
> Dan Seddon wrote:
>> When I choose to use bob deinterlace without XvMC, meaning it must be 
>> using Xv, everything starts off fine then after a short while X starts 
>> to climb in it's processor usage until it's using all that remains after 
>> myth (about %65). It took me a while to catch on to this (it causes 
>> stuttering which after months of trying to get rid of XvMC I wasn't 
>> looking in the right place), it was only when I logged in from my laptop 
>> and did a top that I saw what was going in. Turning off bob-deinterlace 
>> solves the problem - which is bad as you really need bob when displaying 
>> on a montior as I am. I'm sure it's not a processing limitation as in 
>> the worse case all that can be happening is that Xv is splitting the 
>> fields and doubling up the frames on the fly, before scaling up? So, it 
>> has four times the scaling to do - but that shouldn't be an issue to an 
>> Nvidia card. Has anyone seen this and, even better, know how to prevent it?
> Besides the processing you mention, bob also doubles the effective
> output framerate, and so doubles the overhead of the video output thread.
> If "Onefield" deinterlacing (which does the same processing but doesn't
> double the framerate) causes similar issues the problem is elsewhere,
> but if not I'd suspect you're on the hairy edge of required processor power.
> Also make sure you're using a good video sync method (look at
> 'mythfrontend --verbose playback').  OpenGL vsync is good, so long as
> your nVidia driver is not the (79xx? 81xx?) version that sucks down a
> ton of CPU time if you turn that option on.
> -Doug
I was experimenting with de-interlacing/xvmc last night, and found 
something interesting. First off, I am using the mythtv-vid branch, with 
an nVidia 6200 AGP card and a P4 2.93 processor displaying SD video from 
PVRx50 cards, with the latest nVidia drivers (8756). What I found was no 
combination of xvmc/non-xvmc/de-interlacing methods worked acceptably 
(always got prebuffer pauses or buffer underruns) UNTIL I turned off 
OpenGL sync in the frontend settings. After I did that, bob de-interlace 
with XvMC works great, with the very occasional prebuffer pause (1 every 
5 minutes?) and a very watchable picture. With OpenGL sync on, every 
combination I tried had prebuffer pauses every second or so, which 
effectively makes watching anything not very enjoyable. Not sure what 
all that tells us, but I'm happy.


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