What is a WebM file?
WebM is an open, royalty-free video format that Google launched in 2010 for HTML5 video. A .webm file is a restricted version of the Matroska (MKV) container holding VP8, VP9 or AV1 video and Vorbis or Opus audio.
Where WebM files come from
- Screen recorders and web apps that use the browser's MediaRecorder API
- Video downloads from sites that stream VP9 or AV1
- Short loops on forums and image boards, as a lighter alternative to GIF
Where WebM causes trouble
iMovie, Final Cut, QuickTime, older Windows apps, many smart TVs and some upload forms don't accept WebM. Converting to MP4 re-encodes VP8/VP9 video to H.264, since those codecs aren't welcome in an Apple-compatible MP4.
| VP9 in WebM | H.264 in MP4 | |
|---|---|---|
| Royalties | None | Licensed patent pool |
| Efficiency | About 30–40% better than H.264 | Baseline |
| Apple apps | Limited | Full |
| Transparency (alpha) | Supported | Not supported |
Questions
How do I open a WebM file?
Drag it into Chrome, Firefox or Edge, or open it in VLC. Recent Safari versions play most WebM too. For iMovie, QuickTime or older players, convert it to MP4.
Is WebM better than MP4?
For the web, WebM with VP9 or AV1 is efficient and royalty-free. MP4 with H.264 is more compatible. Many sites serve both.
Why are my screen recordings WebM?
Browser-based recorders use the MediaRecorder API, which in Chrome and Firefox records to WebM by default.