i've tried a lot of things to play audio and video in sync. there's one technique that's really reliable and that works on all platforms with gem and/or pdp. i've posted it here a while back - here is it again:
you'll have to split the audio and the video into individual files and play them separately. the best way to make sure that a/v stays perfectly in sync would be to play the audio with [vline~] + [tabread4~] and [snapshot~] the ouput of [vline~] every [gemhead] to determine the frame of the video to be displayed.
the technique above (replace [vline~] with whatever you're controlling your audio playback with) also works for timestretching, reverse playback and scratching. and beside the video and the audio file also a dead_chicken.txt is needed because the framerate of the video needs to be known to pd somehow.
sven.