I answered this question earlier today by advising Deric to trim down the Keynote file he wanted to take a movie from and then go to Share > Export as Quicktime. This method will provide you with a compressed version of the video that you can then drag into iTunes or iMovie.
However, if you want the “pro” method then there’s a way to actually look inside a Keynote “package” and see the individual files it’s made of. In the previous version of Keynote you could control + click to “view package contents”, but now that option has vanished. Try this instead:
(1) Locate the Keynote file in the Finder
(2) add “.zip” to the end of the file name (click “use .zip” when asked)
(3) now double click the zip file and it’ll unpack a FOLDER
(4) inside the folder use QuickLook (tap your space bar) to check through the files
So, whether you’re working with your own Keynote file or someone else’s you can open up all of the assets that were used to construct it, and you can reuse them (within the boundaries of reason and rights, of course).