I was struggeling playing a movie file on iOS with MPMoviePlayerController. The file was just recorded with AVCaptureMovieFileOutput and was called file.avi, located in the Document directory of the app.
The movie player was presented and then immediately disappeared. The URL was correct, the file played without problems on the Mac. Apparently, MPMoviePlayerController expects the file ending to match the file type. Once I renamed the file to file.mov, everything worked as expected.