WebM to MP4
Convert WebM to MP4 so a screen recording or a video saved from the web plays on an iPhone, opens in an editor and uploads without complaint.
How the files you choose are handled is set out in the privacy policy.
How to convert WebM to MP4
- Tap Choose a video and pick the WebM file.
- Leave the choice on Convert to H.264 for an MP4 that plays everywhere.
- Press Convert to MP4 and wait for it to finish, then save the result.
Where WebM files come from
WebM is the open video format built for the web. You rarely choose it. It arrives:
- from browser-based screen recorders and meeting recorders, which save WebM because browsers can write it directly
- from the screen recording tools built into Linux desktops
- from animations and clips saved off websites
- from video editors on the web that export it by default
It plays in Chrome, Firefox and Edge. It does not play in the Photos app on an iPhone, in iMovie, in many versions of Premiere and PowerPoint, or on a good number of TVs. Messaging and social apps often reject it at upload.
Convert or keep: the one choice
A WebM holds video compressed as VP8, VP9 or AV1. MP4 files normally hold H.264. So there are two ways to make the MP4.
| Choice | The video becomes | Plays on | Time taken |
|---|---|---|---|
| Convert to H.264 | H.264, the standard for MP4 | Practically everything | Roughly the length of the video, less on a fast computer |
| Keep the original video | The same VP9 or AV1, in an MP4 wrapper | Recent phones, computers and browsers | About a second |
If the reason you are converting is that something refused the WebM, choose Convert to H.264. Keeping the video is for when you only need the .mp4 name and know the player is modern. VP8 video cannot be kept, because MP4 has no place for it, so it is always converted.
What happens to the sound
WebM sound is Opus or Vorbis. Both are converted to AAC, the sound format MP4 players expect. The difference is not audible in normal use. A WebM with no sound, common for screen captures, gives an MP4 with no sound.
Recordings that will not seek
WebM files written live by a browser recorder often have no duration stored, so players cannot jump to a point in them and show the length as unknown. Converting to MP4 rebuilds the timing information, and the MP4 seeks normally.
Quality and size
Converting to H.264 re-encodes the picture, with settings chosen so the loss is hard to see. The MP4 is often somewhat larger than the WebM, because VP9 is the more efficient of the two. If size matters, run the result through the video compressor. To make a looping picture from the clip, use video to GIF.
Questions
Why will my WebM not play on an iPhone?
The iPhone Photos app and many Apple apps do not support WebM. Converting it to MP4 with H.264 fixes that.
Does converting WebM to MP4 reduce quality?
Converting to H.264 re-encodes the video with a small loss that is hard to see. Keeping the original video loses nothing.
Why is the MP4 bigger than the WebM?
VP9 and AV1 compress better than H.264, so the same picture needs more space as H.264.
My browser says it cannot convert to H.264. Why?
Creating H.264 relies on the browser. Chrome and Edge can do it. In other browsers, choose Keep the original video or switch browser.
Can I convert a long screen recording?
Yes. It takes about as long as the recording runs, and the page has to stay open while it works.
Related converters and guides
- MP4 converterConvert MOV, MKV, WebM, M4V and 3GP videos to MP4.
- MKV to MP4Make MKV videos play on phones, TVs and editors by moving them to MP4.
- Video compressorMake a video small enough to send or post. Pick a quality, or a size such as 16 MB.
- Video to GIFTurn a few seconds of a video into a looping GIF.