In its most simple form, this would be nothing more than taking a movie file and grabbing images at some time interval. I don’t know of any app that can do that; if there is one, please let me know.
A Little workaround I could suggest. Download Camtwist from http://camtwiststudio.com/, load the movie into CT. Now open iStopMotion, select Camtwist as the camera source and define a timelapse duration. Start the timelapse and click play in camtwist.
Thanks for the suggestion.