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MP4
What is an MP4 file?
The video format that plays everywhere. If in doubt, this is the answer.
What MP4 is
MP4 is a container: a wrapper that holds streams encoded by something else. It is used for handing a finished file over, the web and phones.
The extension is .mp4, and the full name is MPEG-4 Video. Both matter less than what the file can hold, which is what the rest of this page is about.
Where MP4 came from
MPEG published it in 2001. The specification is ISO/IEC 14496-14.
Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.
The specification is public
Anyone can implement it without asking permission or paying a licence, which is why it turns up in so many programs and why files written twenty years ago still open.
MP4 is a box, and the codec is what is in it
It usually holds H.264, HEVC, AV1 and AAC. This is the distinction behind most "why will this not play" questions: two files with the same extension can contain entirely different encodings, and a player that refuses one may be perfectly happy with the other.
It also explains why changing container is often fast and lossless while changing codec is neither. Moving the same stream into a different box rewrites the box; re-encoding rewrites the picture.
What else it can carry
MP4 can hold several audio tracks, subtitle tracks and a layout that lets it start playing before it has finished arriving.
That matters mostly when converting: whatever the target cannot hold is dropped, usually without a warning.
What opens MP4
VLC, HandBrake and Adobe Premiere Pro read it, and so do most programs of the same kind.
If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.
Opening it in a browser
Every current browser reads it.
That makes it a safe thing to put on a page or attach to a message without wondering what the other end has installed.
What it can carry besides the content
MP4 can hold document properties.
Whether any of it survives a conversion depends entirely on the target, and the honest answer is usually "some of it".
It is a delivery format
MP4 is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.
The facts, in one place
| Extension | .mp4 |
|---|---|
| Media type | video/mp4 |
| Published by | MPEG |
| First published | 2001 |
| Specification | ISO/IEC 14496-14 |