i'd be super-careful about maintaining AV sync when doing this, but go right ahead if the original is crap and you think you can improve on it. while you're at it, you might as well run some filters on to improve subjective quality. check the avisynth usage forum for inspiration there. can i ask which anime it is? if only ~40% of it was IVTC'd in the original encode, i'd say it's probably from Gainax :) don't be toooo worried about transcoding video - you lose a few high freqs, and theres some rounding error, but it's nowhere near as nasty as transcoding audio... so if possible try to keep the audio track you originally ripped from the DVD.