MP4 to WebM converter

Web developers want royalty-free WebM for <video> tags, and some wikis and chat tools accept only WebM.

Drop a MP4 file hereThe converter loads in your browser.

What happens to your MP4

H.264 video is re-encoded to VP8 and audio to Opus. VP8 is the WebM codec this in-browser engine can encode reliably; VP9 and AV1 encoding are not available in the browser build (they crash or are not compiled in).

Tip: Serve WebM alongside an MP4 fallback: every modern browser plays H.264 MP4, so WebM is an extra, not a replacement.

How to convert MP4 to WebM

  1. Drop your MP4 file on the box above, or tap it to pick one. The engine (about 31 MB) loads once per visit.
  2. The converter reads the file's streams and shows which codecs are inside.
  3. Keep the defaults, or pick a quality and resolution.
  4. Press the button, wait for the progress bar, then download your WebM.

Questions

Why VP8 instead of VP9?

The single-threaded WebAssembly build of FFmpeg we use can encode VP8 stably; its VP9 encoder runs out of memory. For VP9/AV1 use desktop FFmpeg.

Is my MP4 file uploaded?

No. The MP4 is read from your device by FFmpeg running as WebAssembly in the page, and the WebM is written back to your device. No server ever receives it.

Is there a size limit for MP4 to WebM?

We set none. The practical limit is browser memory: roughly 2 GB of output on a computer, and much less on phones.