An MP4 file is a multimedia file commonly used to store a movie or video clip, but may also contain subtitles or images. MP4 is short for MPEG-4 Part 14, which is a container format based on the QuickTime File Format (QTFF) used by .MOV and .QT files.
MP4 files use MPEG-4 compression, a standard developed by the Moving Picture Experts Group (MPEG). This format includes separate compression for audio and video tracks. Video is compressed with MPEG-4 video encoding and audio is compressed using AAC compression, which is the same type of audio compression used in .AAC files.
Much of the MP4 format's popularity can be attributed to Apple's iTunes Store. It is also commonly used for streaming video on the Internet and is supported by a wide range of video programs and various hardware devices.