When playing back some HD or watching live HD through firewire and DVD (VOBs and ISOs) in mythtv (mythtvideo for the ISOs and VOBs) I get a bit of a hitch from time to time, the audio doesn't pause, but it's like the whole scene pauses/slows down for a split second. It only happens on scenes where there is a large movement, for instance when the entire scene is moving (like when lots of people are moving or a car is driving down a street -- I can't describe it properly, but whenever the camera has to track the action of a scene). Its annoying, and I've played with many settings. It doesn't seem to happen when watching livetv or recordings from my QAM or NTSC tuners (I'll check more explicitely soon). I don't get any messages from mythfrontend (no prebuffering pauses or anything) and my CPU isn't even close to high utilization (always less than 60% even when I have these problems).

Seems like a buffering problem of some sort. Happens on 2 of my frontends (haven't tested the third) with nvidia 6150 and 6200 vidcards, using nvidia binaries. The same files play fine with my networked DVD player, so the files themselves or the disk speed aren't the problems. It's some kind fo video rendering problem.

I'm going to test playing some of these files back with mplayer to see if it is a myth specific problem

Any ideas?

The native resolution for both of my TVs is 1024x768, which is what I had my frontends set to (using a vga port for both). Out of curiousity, I also have a laptop front end (resolution 1280x800) which had didn't have any of these problems. I also noted that VLC and mplayer displayed these files fine on the TV. So I took a shot in the dark and changed the resolution to 1280x768 on both of my HDTV frontends and that took care of the problems. I thought I was best off setting the output to match the native resolution of the set...

Any idea why this worked?

Just a guess - but I believe mythtv uses a software scaler. Normally that wouldn't be a problem - but at HD resolutions it just might.