MP4

MP4, officially ISO/IEC 14496-14, is a digital multimedia container format defined as part of the MPEG-4 standard. It extends the ISO Base Media File Format (ISOBMF) to store synchronized audiovisual data, subtitle tracks, still images, and metadata within a single file. MP4 is designed to support efficient streaming and progressive download, making it a common choice for distributing video and audio over both local networks and the Internet.

Internally, MP4 files use a box-based structure. The major boxes include ftyp (file type), moov (the movie box containing metadata and index information), mdat (the media data), and various trak/minf/stbl boxes that define individual tracks and how samples are stored. This organization allows random access, efficient seeking, and compatibility with a range of codecs and bitrates.

Common file extensions are .mp4 for general use; .m4a for audio-only files; .m4v for video. MP4 can contain video encoded with codecs such as H.264/AVC or H.265/HEVC, and audio encoded with AAC, MP3, ALAC, or other codecs. Text and subtitle data may be stored in formats like TTML or WebVTT. The format also supports metadata tagging and streaming-specific features such as fragment-based MP4 (fMP4) for adaptive streaming.

MP4 is widely supported across consumer devices, media players, and software. It is compatible with streaming protocols like MPEG-DASH and Apple HLS when used with appropriate fragmentation. Encrypted MP4 files can be protected with DRM schemes from organizations such as Widevine, PlayReady, and FairPlay.