What is a .mp4 file?
MPEG-4 Part 14 · Video · MPEG · 2001
MP4 is the most universal video format. It is a container that usually wraps H.264 video and AAC audio, a combination that plays on virtually every phone, browser, TV and editor, which is why it is the safe default for sharing video.
What is a .mp4 file used for?
MP4 is a container, not a codec. The extension tells you the wrapper, while the actual video codec inside (most often H.264, sometimes H.265 or AV1) determines quality, size and compatibility.
The classic H.264 plus AAC combination inside an MP4 is about as universal as digital video gets, playing back almost everywhere without extra software.
Because it is streamable and well supported, MP4 is the default export from phones, cameras and editing apps alike.
How to open a .mp4 file
The .mp4 format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .mp4 file.
Windows
- Media Player
- VLC
- any browser
macOS
- QuickTime
- VLC
- Safari
Linux
- VLC
- mpv
- Firefox
Web
- Every modern browser
How to convert a .mp4 file
You can convert a .mp4 file to MOV, WebM, GIF, MP3 using a conversion tool or the export menu of an app that opens it.
.mp4 file signature (magic bytes)
Programs recognise a .mp4 file by the bytes at the start of the file, not by its name. These are the signatures for MP4. For a full breakdown, see the MP4 file signature page.
| Hex signature | Offset | Note |
|---|---|---|
| 66 74 79 70 69 73 6F 6D | 4 | ftyp isom |
| 66 74 79 70 4D 53 4E 56 | 4 | ftyp MSNV |
| 66 74 79 70 6D 70 34 32 | 4 | ftyp mp42 |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .mp4 file?
MP4 is the most universal video format. It is a container that usually wraps H.264 video and AAC audio, a combination that plays on virtually every phone, browser, TV and editor, which is why it is the safe default for sharing video.
Why won't my MP4 play?
The container is MP4 but the codec inside may be one your player lacks, such as H.265. Install VLC, which plays almost anything, or convert the file.
How do I get just the audio from an MP4?
Extract the audio track to MP3 or M4A using a converter. The video is discarded and you keep the sound.