are they downloaded AVIs? if it's stuff like Lost, 24, etc - they're probably converted using DivX - once u re-convert DivX back to DVDMPEG2 the sound goes out of sync - to get around this, i use WinAVi with LOTS of chapters - i.e. 1 every 2 mins. if it's AVI from a digial camcorder - owt will work.