Did you ever figure out a solution? HAving the same problem.
Full motion recording can really make things complicated. I've found that the more you chunk into separate slides the more control you have. Try recording just one task, then stop recording, then press Print screen to create another slide, then record the next task, stop recording etc.
You'll probably end up with lots of slides you have to delete, but each task should be in its own movie--on its own slide. Then record each audio chunk for each task, and voila!
Hope this helps. --Leslie
In addition to what Leslie offered (which is good advice) I've seen others report success by staging the audio to begin slightly after the slide starts. Perhaps .3 .4 or .5 seconds into each slide.
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Here's a 'best practices' trick I've used since C2 days. I duplicate the first slide and add all my "rest of project" graphics. (I call this my "loading slide"). Then I set this slide to about 0.2 seconds and NEVER add audio or an interaction that stops progress to slide 2. The audio starts on slide 2. Then to make sure the audio stops at the end, I duplicate the last slide, remove the audio, and set the "end" slide to 0.2 seconds. I never get any audio lag at the begining or audio crossover when the next file fires up. --Leslie