Convert WebM video — locally, in your browser
Convert WebM to MP4 (and back), trim a clip, or inspect its tracks — processed entirely on your device by your own browser.
What this tool does
WebM is the web-native video container, and now you can convert it without sending it anywhere. The work runs in a Web Worker on your device through the same engine pipeline as every other tool on this site.
Conversion remuxes when the codecs fit the target container and re-encodes through your browser’s WebCodecs encoders when they do not — with honest warnings either way.
How to convert a WebM video without uploading it
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Add the file. Drop your .webm into the home-page tool.
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Choose convert or trim. Pick the target container (MP4) or a time range to keep.
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Download locally. The converted video is saved straight back to your disk.
Supported operations
This list is generated from CompressKit's capability registry — only implemented and tested operations appear here.
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Trim media
Cut a time range without re-encoding where the codec fits.
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Convert format
Change the container (WebM↔MP4) — remux when codecs fit, transcode otherwise.
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Inspect file details
Container and track metadata: duration, resolution, codecs.
Frequently asked questions
- Is my video uploaded anywhere?
- No. The bytes stay in your browser’s worker. The site’s privacy tests assert no request ever carries your video data.
- Why convert WebM to MP4?
- MP4 (H.264) plays everywhere — messaging apps, editors, smart TVs. WebM is smaller and web-friendly. Converting between them locally means no upload for either direction.
- Does it work on iPhone or Safari?
- Inspection works broadly. Encode paths depend on the browser’s codec support and are detected up front — the tool tells you plainly instead of failing silently.
Ready to try it?
The WebM video converter tool runs on this site with no upload step — your file is processed by your own browser and saved back to your device.
Open the WebM video converter tool