And remember: if you're using Windows Movie Maker or iMovie, the files created when you use the Save option in these programs are not video files. They are editable files that are meant to be used with each program. Be sure to Export your final video from either program to ensure you have a video and not an unusable document file. To Export a video from iMovie go to File > Export. To Export using WMM go to Publish Movie > Export to File.