Ello there

I have a few avis that when you seek through them the video goes out of sync with the sound and is always lagging behind, I didn't encode these avis but, would this have to do with the lack of keyframes being in the file?

If this is so how would I go about putting them back in without losing the quaility of the avi?

Btw from what I can tell the files are encoded with divx4 and audio is in mp3 format.