You simply aren't giving enough information here for anyone to help you. And no one has time to go read through a thread that may or may not have anything to do with your problem.
Sounds like your movie app is caching the movies. Which app are you using when the storage space is getting smaller and smaller? Open Setting, go to General, then Usage, then Videos, and see if you see any videos. If so, you can delete by sliding to the left on each one until they are deleted.