File extension

.mp4

MP4 (MPEG-4 Part 14) container

.mp4 files are MPEG-4 Part 14 containers: the near-universal modern container for video and audio, based on the ISO Base Media File Format, holding coded streams such as H.264/HEVC video and AAC audio plus metadata.

Known meanings

Formats and reference material for .mp4

MP4 (MPEG-4 Part 14) container

ISO Base Media File Format container for video, audio, subtitles, and metadata

  • video-animation audio
  • ISO/IEC (MPEG)
Open link

Details

Format notes

MPEG-4 Part 14 (MP4)

MP4 is the dominant container format for digital video and audio today, used everywhere from streaming services and social platforms to phone cameras and video files on disk. It is defined by MPEG as MPEG-4 Part 14 and is built on the ISO Base Media File Format (ISOBMFF), itself derived from Apple’s QuickTime format. Like other containers, MP4 stores coded media rather than defining a codec: a typical .mp4 carries H.264 (AVC) or H.265 (HEVC) video and AAC audio, but it can also hold AV1, subtitles, chapters, and cover art.

Structurally, an MP4 is a tree of “boxes” (also called atoms), each length-prefixed and typed. A moov box holds structural metadata — tracks, sample tables, timing — while mdat boxes hold the media samples. A feature important for the web is “fast-start” (moving the moov box before the media) and fragmentation (fragmented MP4), which enables progressive and adaptive streaming such as MPEG-DASH and HLS.

Adoption And Preservation Notes

MP4’s broad hardware and software support makes it a safe, long-lived choice for distributing and storing media, though its codecs (notably H.264/HEVC) can carry patent-licensing considerations, which is part of why royalty-free alternatives like WebM/AV1 exist. Because the video is usually lossy, keep a high-quality master for preservation and record the contained codecs and profiles. The common media type is video/mp4 (or audio/mp4 for audio-only).

Security Notes

As a box-structured binary format, MP4 demuxers should validate box sizes and sample-table offsets from untrusted files, since malformed atoms have repeatedly been a source of media-parser vulnerabilities.

Further Reading

  • ISO Base Media File Format (ISO/IEC 14496-12) overview: https://en.wikipedia.org/wiki/ISO_base_media_file_format