Most of our videos include two file formats: QuickTime (.mp4 file extension) and Windows Media (.wmv file extension). They both play the same video. Download the file format that you prefer. Some videos use .m4v as the QuickTime extension. We do this for some “chapterized” videos to give them backward compatibility with QuickTime Player 7.xx. This extension should play with all versions of QuickTime. If you have a playback problem, renaming the extension to .mp4 usually works. Some of our titles also include documents in Acrobat PDF format or ZIP.