I used to have a similar problem. Audio and video can drift out of sync
as they are often clocked by independent oscillators.
The solution is a hassle but not too bad. The good news is that
you don't have to recapture it if you still have the iMovie project.
Within iMovie, break up the movie into segments. Ideally, make
the breaks at scene changes. Try to keep the clips shorter than
five minutes. You may need more or less time depending on your
degree of drifting but this will probably be fine.
Once you have your movie segments. Use the iMovie "extract audio"
function for each segment (except the very first segment which won't
matter). You can go to the timeline view to better see what is happening.
This step will separate audio from video and lock the audio segment to the
video segment at the beginning (you'll see little pushpins in the time line).
Now, you can create your DVD with iDVD. All should be fine. The
audio/video will be resynchronized at the beginning of each clip.
You probably won't even notice it happening; it will just work fine.
One other note:
I'm not totally familiar with Miglia directors cut but I don't doubt
that it is similar to the Canopus ADVC converters which I have used.
The ADVC converters have a jumper setting for "locked audio" which
locks the audio clock to the video clock. Counterintuitively, I had to
"unlock" my setting for my audio/video sync problem to go away.
You may want to look for such a setting on your Miglia hardware.
You may be able to avoid this extra work all together.
