An extremely popular movie format on the Web, which is officially Part 14 of the MPEG-4 standard. MP4 files are supported by most software media players and many Blu-ray/DVD players as well. They are a common format for movie downloads, and Blu-ray players with front-panel USB ports are generally capable of playing MP4 movies directly from a USB drive.Using the .MP4 extension, MP4 files are containers that hold multimedia objects (audio, video, images, animations, menus, etc.) and support video compression codecs such as H.264. See MPEG, H.264, M4V and MP4 player.