MP4 file format
MP4 is the safe answer to "what format should I send this in?" — phones, TVs, browsers, editors and messengers all play it without a second thought.
or drag & drop them here · images, video, audio and documents · up to 2 GB
What is MP4?
MP4 was standardised in 2001 as MPEG-4 Part 14, built directly on Apple's QuickTime file format. It is a container, not a codec: a wrapper that holds video, audio, subtitles and chapter markers and describes how they line up in time. The near-universal combination inside is H.264 video with AAC audio, which is what most people actually mean when they say "MP4".
That container/codec split explains the one failure people hit. A file can be a perfectly valid MP4 and still refuse to play, because the video inside is H.265/HEVC or AV1 rather than H.264. The device opens the box, does not recognise what is in it, and gives up. Re-encoding the video stream to H.264 fixes it while keeping the same .mp4 extension.
MP4 was also designed for streaming. Its metadata index can sit at the front of the file so playback starts before the download finishes, and the fragmented variant underpins DASH and HLS, the systems behind virtually every video platform. That combination of streaming support and universal decoding is why MP4 became the default of the entire web.
| Extension | .mp4 |
|---|---|
| Category | Video |
| MIME type | video/mp4 |
| Released | 2001 |
| Developed by | ISO/IEC MPEG |
| Compression | Container (depends on codec) |
MP4: frequently asked questions
- Is MP4 a codec or a container?
- A container. MP4 defines how video, audio and subtitle streams are packed together, not how they are compressed. The compression comes from the codec inside — usually H.264, sometimes H.265 or AV1. Two MP4 files can therefore behave completely differently on the same device.
- Why will my MP4 not play on this device?
- Almost always because of the codec inside rather than the container. Modern phones record H.265/HEVC, which older TVs, players and editing software cannot decode. Converting the video stream to H.264 keeps the .mp4 extension and makes the file play everywhere.
- MP4 or MOV — what is the difference?
- Very little structurally: MP4 was derived from Apple's MOV format and they share the same underlying design. MOV allows some Apple-specific extras like ProRes, while MP4 is the neutral international standard. For sending files to other people, MP4 is the safer pick.
- How do I make an MP4 smaller?
- Lower the resolution if it exceeds what will actually be watched, then reduce the bitrate — those two dominate file size. Switching from H.264 to H.265 roughly halves the size at equal quality, but costs compatibility, so only do it when you control the playback device.
- Can an MP4 hold subtitles and several audio tracks?
- Yes, though support is patchy. MP4 can carry multiple audio tracks and timed-text subtitles, but many players expose only the first audio track and ignore embedded subtitles. If subtitles matter, keep a separate .srt file alongside the video.
- Why is MP4 recommended for sharing?
- Because it is the one format you can send without asking what the recipient uses. Every browser, phone, TV, console and messenger decodes H.264 in MP4. Any other container introduces a chance the file simply will not open on the other end.