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.
What opens 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.
Windows
- Media Player
- VLC
- any browser
macOS
- QuickTime
- VLC
- Safari
Linux
- VLC
- mpv
- Firefox
Web
- Every modern browser
Open a .mp4 file step by step
- Confirm the file really is a .mp4. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Media Player or VLC.
- On Mac, use QuickTime or VLC.
- On Linux, try VLC or mpv.
- Still stuck? Convert the .mp4 to MOV, which opens more widely.
Why can't I open my .mp4 file?
Almost always because no installed app understands MP4. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .mp4 at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .mp4 file
You can convert a .mp4 file to MOV, WebM, GIF, MP3.
HandBrake handles MP4 to WebM and MOV to MP4 with a preset. Every re-encode is lossy, so if you only need a different container, use ffmpeg -c copy and skip the quality hit.
What is the .mp4 file signature (magic bytes)?
A .mp4 file carries the hex bytes 66 74 79 70 69 73 6F 6D at offset 4, which read as ftypisom in ASCII. Programs identify MP4 by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for MP4. For a full breakdown, see the MP4 file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 66 74 79 70 69 73 6F 6D | 4 | ftypisom | ftyp isom |
| 66 74 79 70 4D 53 4E 56 | 4 | ftypMSNV | ftyp MSNV |
| 66 74 79 70 6D 70 34 32 | 4 | ftypmp42 | 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.