[mythtv-users] image choppy in mythtv but pvr150's seem ok

[jos]

I posted this question on http://www.mythtvtalk.com/ quite some time
ago, but have not gotten any reply yet (just a lot of views).
Furthermore I could not find any post matching 'my problem' in this
list's archive, so, I thought I'd 're'-post my question here.

I have 3 hauppauge pvr 150's in my computer and they output a good
quality image if I use them as raw video devices and pipe the data to
vlc like this:

cat /dev/video0 | cvlc -

I can do this for video1 and video2 at the same time and I get three
nice images.

cat /dev/video0 | cvlc - &
cat /dev/video1 | cvlc - &
cat /dev/video2 | cvlc - &

I get similar results if I pipe the data to mplayer (svn r34540)

The images are never choppy, so this proves that the graphics card and
the cpu are capable of processing the data produced by the three devices.

However if I start up the mythtv frontend and I want to watch live tv or
if I make a recording, the live images and / or the recording turn out
to be choppy. I sometimes get the impression that this is linked to the
content of the images. If they are bright the image gets choppy,
otherwise it doesn't. But this is not always the case. Furthermore it
seems that not all channels show the same amount of choppyness as others do.

I'm using mythbuntu based on Ubuntu 12.04.1 LTS, I'm running kernel:
Linux mythtv 3.2.0-35-generic #55-Ubuntu SMP Wed Dec 5 17:42:16 UTC 2012
x86_64 x86_64 x86_64 GNU/Linux on a AMD Athlon(tm) 64 Processor 3200+
The frondend version is mythfrontend version: fixes/0.25
[v0.25.2-15-g46cab93] www.mythtv.org
The backend is mythbackend version: fixes/0.25 [v0.25.2-15-g46cab93]
www.mythtv.org
My video card is a NVIDIA Corporation NV18 [GeForce4 MX 4000] (rev c1)
(prog-if 00 [VGA controller])


I used to run these 3 cards on the same hardware without a problem, but
after an update that did not appear too suspicious to me, things got
broken. Going back to an old version did not prove to be a solution. The
lastest and greatest mythbuntu also did not solve the problem. Question:
can anybody give me a hint as to where the problem might lay or what is
causing it?

Cheers!