What is MP4?
MP4 is a multimedia container in the ISO Base Media File Format family. It can hold multiple timed tracks, subtitles/captions, metadata and alternate presentations in addition to ordinary video and audio.
What can an MP4 contain?
| Layer | Examples |
|---|---|
| Video | H.264/AVC, HEVC/H.265, AV1 and other registered sample entries/profiles |
| Audio | AAC, ALAC and many other mapped audio formats |
| Other timed tracks | Subtitles/captions, timed text, metadata and alternate media tracks |
| File metadata | Names, artwork, dates, language, location and application-specific metadata |
Important MP4 / ISO-family capabilities
- Multiple audio/video tracks: more than one media track can be stored in the same file.
- Alternate groups: tracks can be grouped as alternatives, such as several languages or a spatial-audio track with stereo fallback.
- Subtitle/caption tracks: supported through defined sample-entry formats and profiles.
- Edit/timing structures: track timing and edits are represented independently from codec compression.
- Fragmentation: fragmented MP4 is widely used for streaming and segmented delivery.
- HDR signalling: modern MP4-family workflows carry colour/mastering metadata and widely used HDR/Dolby Vision signalling.
- Sample-entry identifiers: four-character entries such as
avc1,hvc1,hev1andav01identify media mappings within the container.
Exact feature availability depends on the ISO/industry profile and application. MP4 is a family of interoperable conventions, not a promise that every player accepts every possible track combination.
MP4, MOV and ISOBMFF are related but not identical
MP4 grew from the same structural family as Apple QuickTime/MOV and ISO Base Media File Format. They share box/atom-style structures and many concepts such as tracks and alternate groups, but they have different registrations, conventions and ecosystem expectations.
Does MP4 determine quality?
No. Quality depends primarily on the encoded streams: codec, bitrate, resolution, frame rate, chroma, bit depth and source. Remuxing compatible streams from MKV or MOV into MP4 can leave the audio and video data unchanged.
Common confusion
MPEG-4 and MP4 are not synonyms. MPEG-4 is a family of standards. MP4 is one container format from that family. MPEG-4 Part 2 is also a video coding standard, which is a different layer again.
avc1 is not “another codec.” It is a four-character sample-entry identifier for AVC/H.264 in ISO-family files. See FOURCC and four-character identifiers.