Cell phones create HUGE video files. Every year or so I copy my new phone videos to a hard drive and then use the "find" command in Linux to find .mp4 and .mov files, execute ffmpeg on them, outputing them to an .m4v files do I know wich ones are the new files. Note: .m4v = Apple's own extension for .mp4 because Apple refuses to get along with the rest of the world. It's the same file format. You can rename them all to .mp4 once you're done.