Is my video uploaded to a server?

No. The conversion runs entirely in your browser with WebCodecs. Your video stays on your device, and once the page has loaded it even works offline.

What codec does the WEBM use?

Video goes to VP9 and audio to Opus, the standard pair for WEBM. VP9 works in Chrome and Firefox, so it's the most reliable in-browser video target.

Why is the converted file sometimes larger than the MP4?

MP4s are usually H.264, already heavily compressed. Re-encoding to VP9 at good quality can land at a similar or slightly larger size. What you get is an open, royalty-free WEBM, not necessarily a smaller file.

MP4 to WEBM

Re-encodes your MP4 to VP9 video and Opus audio for the WebM container, all on your machine.

What this does

Convert MP4 video to WebM. The video is re-encoded to VP9 and the audio to Opus, the standard pair for the WebM container, entirely in your browser with WebCodecs.

How it works

1Drop your MP4 or pick it from your device.
2Click Convert to WEBM. The video is re-encoded to VP9 + Opus right in your browser.
3Download the WEBM when encoding finishes.

Built with open source

Mediabunny — Converts and edits video and audio in the browser via WebCodecs. Add-on encoders cover MP3, AAC, and FLAC. · MPL-2.0

Frequently asked questions

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