Convert MP4 to WebM Online — No Upload, No Watermark
WebM (VP9 + Opus) is the open royalty-free format that Chrome, Firefox, and Edge prefer for web video. Converting MP4 to WebM is useful when you want a smaller file for a website or want to avoid H.264 licensing.
Drag & drop your video here, or click to browse
Max file size: ~2 GB (memory permitting)
Where MP4 files come from
The move to WebM is almost always for the web: VP9 in WebM is meaningfully smaller than H.264 for the same quality, which matters when a video is a page asset rather than a download.
What changes when you convert MP4 to WebM
| Video | H.264 re-encoded to VP9 |
|---|---|
| Audio | Re-encoded to Opus |
| File size | Typically 25 to 35 percent smaller at matching quality |
Worth knowing first
VP9 encoding is slow, several times slower than H.264, and it all happens on your own processor here. A long clip takes real time. Also check where the file is going: Safari only gained VP9 recently and some older smart TVs and editors still refuse WebM entirely.
FAQ
Why is this conversion so much slower than the others?
VP9 does far more work per frame than H.264 in exchange for smaller files, and the encode runs on your CPU in this tab rather than on a server. Expect several times the wait of an MP4 conversion, and more again for 4K.
Should I serve WebM or MP4 on my site?
Both, if you can. Offer the WebM first in a video element with an MP4 fallback after it, and browsers pick what they support. If you can only ship one file, MP4 remains the safer single choice.
Does WebM support transparency?
Yes, VP9 carries an alpha channel, which is the main reason to use WebM for overlays and animated graphics on the web. An MP4 source has no transparency to preserve, so the conversion cannot create it.
Is this MP4 to WebM converter really free and without upload?
Yes. The tool runs entirely in your browser using FFmpeg compiled to WebAssembly. Your MP4 file never leaves your device — open the DevTools Network tab to verify zero uploads. No signup and no watermark. The practical size limit is the memory your browser gives this tab, which is generous on a computer and a few hundred megabytes on a phone.