Convert MP4 to WebM
Convert MP4 to WebM online free: phone and camera videos become small VP9 WebM files for websites. Many at once, nothing is uploaded. No sign-up, no watermark.
MP4
MP4 is what phones, cameras and most apps record and share: almost always H.264 or HEVC video with AAC sound.
An MP4 plays nearly everywhere, but websites and some tools want a smaller WebM, an animated GIF or just the sound as MP3.
MP4 to WebM: remux or re-encode
MP4 to WebM is always a re-encode: WebM holds VP9 (or VP8, AV1), not the H.264 or HEVC inside the MP4. Your browser’s VP9 encoder does the work, the sound becomes Opus.
At the Original preset a 1080p minute becomes about 45 MB of VP9, usually less than a phone’s MP4. VP9 encoding is slower than playing the video; a 4K clip takes several times its length.
How it works
- Drop one or more MP4 files: WebM is already selected. Quality, maximum resolution and sound can be changed before you start.
- Streams that fit WebM are copied; anything else is re-encoded with WebCodecs, or FFmpeg compiled to WebAssembly when the browser can’t.
- Download each file, or all of them as one ZIP.
Questions
Are my videos uploaded?
No. Reading, remuxing and encoding all run in this browser tab. Open DevTools and watch the Network tab while a file converts: no request carries it.
Why is one file done in seconds and another takes minutes?
A remux only copies the streams, so it runs at disk speed. A re-encode decodes and encodes every frame; FFmpeg in WebAssembly, used when the browser can’t, is slower still.
How large can a video be?
Up to 3 GB per file for free, and as many files as you like. Remuxes and WebCodecs re-encodes stream from the disk; the FFmpeg path holds the result in memory.