WEBM file format
WebM is Google's open video format for the web: royalty-free, natively supported by browsers, and the only common format that keeps transparency in video.
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What is WEBM?
Google released WebM in 2010, shortly after buying the company behind the VP8 codec. The goal was a video format the entire web could use without licence fees, at a time when H.264 patent terms made browser vendors nervous. A WebM file pairs VP8, VP9 or AV1 video with Vorbis or Opus audio, all of them open and free to implement.
Its home is the browser. HTML5 video plays WebM natively in Chrome, Firefox and Edge, and Safari eventually joined for VP9 and AV1. Browser-based recorders lean on it too: OBS, Loom, screen-capture extensions and the MediaRecorder API all produce WebM by default, which is why so many people first encounter the format after recording their own screen.
VP8 and VP9 support an alpha channel, so a WebM can have a genuinely transparent background — something MP4 cannot do in any widely supported way. That makes it the practical choice for overlay animations on websites. Outside browsers the picture flips: TVs, editors, phones' native players and social platforms often reject WebM entirely.
| Extension | .webm |
|---|---|
| Category | Video |
| MIME type | video/webm |
| Released | 2010 |
| Developed by | |
| Compression | Container (depends on codec) |
WEBM: frequently asked questions
- What is WebM actually for?
- Playing video inside web pages without licence fees. It was built for HTML5 video and browser tooling, and that is where it excels. For anything outside a browser — sending a clip to a friend, importing into an editor, playing on a TV — MP4 is the format that works.
- Do iPhones and Safari play WebM?
- Partially. Safari added VP9 and AV1 support in recent versions, so many WebM files now play, but older Apple devices and some in-app browsers still fail. If your audience includes iPhones, serve MP4 as a fallback source alongside the WebM.
- WebM or MP4 for my website?
- Offer both if you can: WebM often produces a smaller file at the same quality, and MP4 guarantees playback everywhere. The HTML5 video element accepts multiple source elements and picks the first one the browser understands, so you do not have to choose.
- Can WebM have a transparent background?
- Yes, and it is one of the format's few unique advantages. VP8 and VP9 support an alpha channel, so animated overlays keep their transparency in the browser. Converting such a file to MP4 flattens the transparency, usually onto a black background.
- Why did my screen recorder save a WebM file?
- Because browser-based recording tools use the MediaRecorder API, which outputs WebM by default. Loom, OBS browser sources and most screen-capture extensions do the same. Converting to MP4 is the standard step before editing or sharing the recording.
- Does converting WebM to MP4 lose quality?
- A little, because the video is re-encoded from one lossy codec to another. Keep the original resolution and use a generous bitrate and the loss stays invisible in practice. Any transparency in the source will not survive the conversion.