Video format
What is a .mp4 file?
MP4 is the most widely used video format. It’s a container: it holds a video track, audio tracks and metadata, and the codec inside decides the quality and the size.
With H.264 video and AAC audio an MP4 plays on nearly any phone, TV, browser or editor, which makes it the safe choice for sharing video.
fileclay opens and writes MP4
MP4 vs MOV vs MKV
| MP4 | MOV | MKV | |
|---|---|---|---|
| Developer | ISO | Apple | Matroska project |
| Codecs | Most modern ones | Most, plus ProRes | Almost any |
| Subtitles | Basic | Basic | Full tracks |
| Browsers | All | Limited | Limited |
| Best for | Sharing and the web | Editing on Apple | Films with many tracks |
When to use MP4
Good for
- Sharing video on any platform
- Uploading to YouTube, Instagram or TikTok
- Playing on TVs and phones
Not a good fit
- Keeping several audio and subtitle tracks: MKV handles them better
- Professional editing masters
- Video with transparency
How to open .mp4 files
| Platform | App | Notes |
|---|---|---|
| Windows | Media Player | Built in |
| macOS | QuickTime Player | Built in |
| iPhone, iPad | Photos, Files | Built in |
| Android | Google Photos, Files | Built in |
| Browsers | Chrome, Safari, Firefox, Edge | Plays H.264 files directly |
| Any system | VLC | Plays nearly every codec |
Convert MP4 files
From MP4
All 46 output formats: .webm, .mkv, .avi, .mov, .gif, .m4v, .mpeg, .mpg, .ts, .m2ts, .mts, .m2v, .mxf, .ogv, .flv, .vob, .wmv, .asf, .divx, .3gp, .3g2, .ivf, .mp3, .wav, .m4a, .m4b, .ogg, .oga, .opus, .aac, .flac, .aiff, .aif, .wma, .ac3, .mka, .caf, .au, .tta, .wv, .mp2, .png, .jpg, .jpeg, .webp, .bmp
Conversions run in your browser. Files aren’t uploaded.
How to identify a .mp4 file
MP4 is built from boxes. The first one starts at the fifth byte and is labelled “ftyp”. MOV shares this structure.
It’s read here, in your browser. Only the first bytes.
Your file
What comes after
Questions about MP4
Why won’t my MP4 play?
Usually because of the codec inside, not the container. H.265 or AV1 may need a newer player. VLC opens nearly all of them.
Is MP4 the same as H.264?
No. MP4 is the container and H.264 is the video codec inside it. An MP4 can also carry H.265 or AV1.
Is MP4 better than MOV?
For sharing, yes: it plays in more places. Quality depends on the codec, not on the container.
Does converting to MP4 lose quality?
Not if the tracks are only copied into the new container. It does if the video is encoded again.
What is “fast start” in MP4?
It puts the index at the start of the file so that video can play before it has fully downloaded.