MP4 file format

MP4 (formally MPEG-4 Part 14) is a digitalmultimediacontainer format most commonly used to store video and audio, but it can also be used to store other data such as subtitles and still images. Like most modern container formats, it allows streaming over the Internet. The only filename extension for MPEG-4 Part 14 files as defined by the specification is .mp4.

MP4 is derived from the ISO Base Media File Format, which in turn is based on the structure of the QuickTime File Format. The format organizes a presentation into tracks containing timed samples and associated metadata. Its underlying structure is composed of hierarchical data structures known as boxes (also called atoms in QuickTime terminology), which describe the contents and organization of the file. This structure allows MP4 files to support local playback, editing, progressive download, and streaming applications.

The MP4 format is widely used for distributing and storing audiovisual content because it can combine video, audio, subtitles, metadata, and other data within a single file. Common combinations include H.264/MPEG-4 AVC video with Advanced Audio Coding audio, although the MP4 container is not limited to these codecs. The format is also used in Internet and multimedia applications where its support for progressive download and fragmented files is useful.

The filename extension defined for MPEG-4 Part 14 files is .mp4. Other extensions, such as .m4a, .m4v, and .m4b, are commonly associated with particular types or uses of files based on the ISO Base Media File Format, but they should not be confused with separate container formats.

MPEG-4 Part 14 is one part of the broader MPEG-4 family of standards. It specifies the MP4 file format itself, while other parts of MPEG-4 specify technologies such as audio and video coding. The current edition of the MP4 file format standard is ISO/IEC 14496-14:2020.

During the 2000s, portable media players were sometimes marketed as "MP4 players". The term was often used generically for portable video players and did not necessarily mean that the devices supported the MPEG-4 Part 14 container; some instead supported other formats such as AMV.