Convert WebM to MP4 online
WebM plays in browsers but not in iMovie, Premiere, WhatsApp or on iPhone. Turn it into a universal MP4 (H.264/AAC) without installing anything — the conversion runs in your browser with FFmpeg.
Your files never leave your browser
How to use
- 1
Drop your WebM file into the box, or click to choose it.
- 2
Wait for the conversion — a compatible stream is remuxed in seconds, otherwise it is re-encoded.
- 3
Download the MP4, or process several files and grab a ZIP.
FAQ
Is the video uploaded?
No. FFmpeg runs as WebAssembly in your browser; the file never leaves your device. Premium can process files up to 4 GB on our servers instead.
Will quality drop?
If the WebM already holds H.264 video it is copied bit-for-bit. Otherwise it is re-encoded at CRF 23, which is visually indistinguishable for most footage.
How long does it take?
Remuxing takes seconds. Re-encoding runs at roughly real time on a laptop; a 10-minute clip takes around 10 minutes.
Is there a size limit?
Up to 2 GB in the browser, limited by device memory. Premium raises it to 4 GB with much faster server processing.
Are subtitles kept?
Embedded subtitle tracks are dropped — MP4 handles them poorly. Extract them beforehand if you need them.