Convert MP4 to WebM
The web's own video format, made from your MP4 — encoded privately on your device, nothing uploaded.
Drop your video or audio here
or
MP4, MOV, WebM, MKV, AVI, MP3, WAV and more — any size, no upload
🔒 Files never leave your device — everything runs in your browser.
WebM is the video format the open web standardized on: HTML pages embed it without licensing questions, every current browser plays it, and open-source projects prefer it on principle. When a site, a documentation page, or a platform asks for WebM, this conversion turns the MP4 you have into the format they want.
The conversion re-encodes the video and audio with WebM's modern open codecs (VP9 with Opus on most browsers), entirely in your browser. Re-encoding takes real time on longer videos, and the result is typically comparable to the MP4's size at matching quality. The file itself never uploads anywhere at any point.
How it works
- Drop your file
Any common format, any size. Nothing is uploaded — the tool runs in your browser.
- Convert
Compatible files are repackaged instantly with zero quality loss; others are hardware-transcoded at high quality.
- Download
Your converted file is ready on your device — nothing to wait for, nothing to delete from a server.
Frequently asked questions
Why does MP4 to WebM take longer than other conversions?
Because nothing can be copied — MP4's codecs are not allowed inside WebM, so every frame and sample is genuinely re-encoded into WebM's own. Speed depends on your device; the progress bar and time estimate keep it honest.
Will the WebM be smaller than my MP4?
Often slightly, sometimes not — VP9 is efficient, but the outcome depends on how tightly the MP4 was already compressed. WebM's win is openness and web-native playback, not guaranteed size savings.
Where does WebM actually work?
Every current browser on every platform, plus most modern video tools. Where it lags is older TVs, car systems, and Apple's pre-2020 software — for those destinations, MP4 remains the safer format.
Is my file uploaded to a server?
No. ConvertUno runs entirely in your browser on your own device. Your file never leaves your computer or phone — there is no upload at all.
Is it really free, with no watermark?
Yes. Processing happens on your device, so serving you costs us almost nothing — no watermark, no account, no file-size limit, no daily quota.