Video on some games is herky jerky or lsort of
Ok, well i have seen this many many times, and as far as i can tell quite a few things can cause it.. from the CPU getting "Bogged Down" with an algorithm, to, difficulty in reading the Media, to, not enough memory, bad memory management and so on.. Sometimes it can be fixed by cleaning the DVD, if used. But often it is simply a "Glitch" however if it happens repeatedly at the same spot in a game, or whatever, then it maybe damaged media. Again if DVD a Lens Cleaner may be used this indeed may help, don't over do the cleaning though as it will damage it more than help. If streamed from a HDD, then there maybe damaged sectors tracks blocks etc, if this is suspected, then uninstall and reinstall the software, after doing a disk cleanup and scan, this too will often sort problems like this out too.
The sound is often encoded away from the video data, and so good sound, doesn't always mean anything, as the sound may indeed be OK, but the picture terrible.
If run on a PC, More RAM, Higher GPU and CPU speeds, more swap space, will usually sort most problems out.