MP4 to WebM
Convert MP4 to WebM online for free — re-encode MP4 videos to WebM with VP9 video and Opus audio, the open format used for web pages, HTML5 video and background videos. Runs privately in your browser using its built-in encoders.
100% private — your video is processed on your device, never uploaded. Conversion happens on your device; nothing is uploaded.
If the video and audio are already compatible they are copied without re-encoding (fast and lossless); otherwise they are converted.
Processing uses your browser’s built-in video encoders (WebCodecs) through the open-source Mediabunny library — your video is never uploaded. Works best in recent Chrome, Edge and Safari; the output is kept in memory, so very large files (several GB) may need a computer with plenty of RAM.
How to convert MP4 to WebM
- Drop your MP4 file in the box.
- Click Convert to WebM.
- Preview the WebM.
- Download it.
What you can use it for
- Make open-format video for websites
- Create HTML5 background and hero videos
- Prepare clips for web apps and games
- Offer a WebM source alongside MP4
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Why use WebM?
WebM with VP9 is an open, royalty-free format with excellent compression, supported by Chrome, Edge, Firefox and modern Safari.
Is WebM smaller than MP4?
Often — VP9 is usually more efficient than H.264 at the same quality, though results vary by video.
Is my video uploaded?
No. The video is read and encoded by your own browser using its built-in video encoders, so it never leaves your device — even large or private videos stay private.
Is there a file size limit?
There's no upload limit. The finished video is held in memory before download, so files up to a few GB work on most computers; very large files need more RAM.
Which browsers work?
Recent Chrome, Edge and Safari work best (they have hardware video encoders). Firefox 130+ works for most files.