WebM to MP4 Converter

Upload a WebM video to convert it to MP4, entirely in your browser. Pick a quality preset, optionally cap the resolution to keep the file light, and download an MP4 (H.264 + AAC) that plays on almost any device or program. Nothing is uploaded to a server, and the video is gone as soon as you close or refresh this tab.

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Frequently asked questions

Is my video uploaded to a server?

No. All conversion (decoding the WebM and re-encoding to MP4) happens in your browser via WebAssembly (ffmpeg.wasm). The video never leaves your computer, and it isn't saved anywhere - it's gone as soon as you close or refresh this tab. The only thing your browser downloads is the conversion engine itself (an open-source library, not your file), the first time you use the tool.

Why convert from WebM to MP4?

MP4 with H.264 video and AAC audio is the most compatible format: it plays on iPhone/iOS, video editors, PowerPoint, WhatsApp and practically any device or program. WebM (common for screen recordings, browser captures or webcams) doesn't always play well outside Chrome or Firefox.

Why is the MP4 sometimes larger than the original WebM?

WebM usually uses the VP9 (video) and Opus (audio) codecs, which compress slightly better than H.264/AAC (used by MP4) at similar visual quality. It's normal for the converted file to end up a bit heavier. If size matters, try the "Smaller file" preset or cap the max resolution.

Is there a size or length limit?

A max of 500MB is recommended to keep processing manageable, since everything happens in your device's memory. Long or high-resolution videos may take a while and use a fair amount of memory depending on your device.

Why does the conversion take so long?

Conversion runs entirely in your browser, on a single CPU thread, without using your GPU or any external server. It's slower than a desktop converter or a cloud service, but in exchange your video never leaves your computer.

Does it work in any browser?

You need a browser with WebAssembly support (every modern browser: Chrome, Firefox, Edge, Safari). On phones, large files may be slow or run out of memory depending on the device.