I have a .mov file that I saved out from Flash 5.5. When I view in QuickTime it looks great. When I place into Storyline as video and hit Preview, the video is much longer. It takes several seconds for the video to begin moving as if there are extra frames added.
I am now saving off as SWFs and inserting as video which seems to look cleaner and gets around these issues.
Still, I want my videos to be seen by all devices/HTML5.