jit.qt.movie adding audio track

I am having a hard time syncing music to a qt video. Basically I have a
H.264 coded video, and 192kbit 44.1 mp3 audio. I read them both into
separate tracks of jit.qt.movie. At the start they are tight, but towards
the end the movie starts lagging behind. So I fiddled with the movie
"duration" a little to match the ending, and then flattened the movie.

Now the resulting movie keeps on having the same timing issues. In the
beginning its tight, towards the end (5min) the video lags about 0.5sbehind.

What I don’t understand is that if I interrupt the movie (by pause or the
timeline) the audio and video are lined up again. This goes for both the
flattened movie and the editing process in jitter (using the frame message
to jump).

Am I overlooking something obvious? Can I make the sound and video
interlaced maybe? Thanks.

Thijs