WebM to MP4 converter

Screen recorders, browser downloads and MediaRecorder save WebM, which iPhones and many editors handle poorly.

Drop a WebM file hereThe converter loads in your browser.

What happens to your WebM

VP8/VP9 video cannot be stored in a standard MP4 that Apple devices play, so the video is re-encoded to H.264 and Opus/Vorbis audio to AAC. AV1 WebM is also re-encoded for compatibility.

Tip: Screen recordings with variable frame rate are normalised during the re-encode, which fixes the audio drift some editors show on WebM.

How to convert WebM to MP4

  1. Drop your WebM 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 MP4.

Questions

Why is WebM to MP4 slower than MOV to MP4?

WebM uses VP8/VP9, which must be fully decoded and re-encoded to H.264. That is real computation, done on your own CPU.

Will it play on iPhone afterwards?

Yes, H.264 + AAC in MP4 plays on every iPhone and iPad.

Is my WebM file uploaded?

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

Is there a size limit for WebM to MP4?

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