[MacDV] Editing w/Voice Over

[KS]

It's been a while since I've been asked to edit a training piece on  
iMovie with voice over.  I seem to remember that if you want  
transitions like dissolves, etc.  there's some "trick" to editing so  
the video and V.O. don't get out of synch.  I believe it has to do  
with adding frames to compensate for the amount of scene you lose  
when applying a transition.

The last time I tried editing with V.O. I had the video and audio  
synched perfectly – then when I applied dissolves and fades  
throughout the 10 minute piece – the whole movie was out of synch.    
After many attempts to fix the synch, I gave up and took them all  
out.  The result was a "cuts only" movie.

Is there a simply way to compensate for this synch problem when you  
want dissolves and other transitions throughout the movie and still  
have everything in synch?

Someone told me, "just add a couple of frames on the back and front  
of each scene."  But, that doesn't give me a step-by-step process to  
follow.  I would really appreciate a more detailed "how to" on this,  
please.

Thanks in advance,

Karl