Private by design
Nothing is uploaded.Unlike most online converters, your video is never sent to a server. It is converted in your browser tab and stays on your device.
WebM to MP4
Convert WebM to MP4
Drop in a WebM and get an MP4 back. The conversion happens in your browser - nothing is uploaded.
Lots of screen recordings and browser captures come out as WebM, which some editors, chat apps, and upload forms still reject. Most "WebM to MP4" sites fix that by uploading your video to their server. This one does not: it converts the file on your own device using ffmpeg compiled to WebAssembly, so the video never leaves your computer. Free, no signup, no watermark. It is the same private, local-first approach as our screen recorder.
Nothing is uploaded. The file is converted on your device.
Choose a video or drop it here
WebM, MOV, MKV, AVI and more. Nothing is uploaded.
No install, no signup
Just a web page.No app, no extension, no account, and no watermark on the result. Works on locked-down work and school computers too.
Standard MP4
H.264 + AAC.Get a widely compatible MP4 (H.264 video, AAC audio) that editors, chat apps, and upload forms accept.
How it works
Three steps, all in the browser. The first conversion downloads the ffmpeg engine (about 30 MB) once; after that it is instant to start.
- Choose your video. Drop a WebM (or MOV, MKV, AVI) onto the box, or click to pick one. It is read straight from your device - not uploaded.
- Click Convert to MP4. The video is re-encoded to H.264 + AAC in your browser. A progress bar shows how it is going.
- Download the MP4. Preview the result, then download it. Nothing was ever sent anywhere.
When this helps
- A screen recording saved as WebM that you need as MP4 for an editor, an LMS, or a chat that rejects WebM.
- A private or sensitive clip you would rather not upload to a random conversion website.
- A managed laptop where you cannot install a desktop converter or a browser extension.
- A quick one-off where opening heavy video software is overkill.
Recording something new?
If you have not recorded yet, you can skip the conversion entirely: our screen recorder can save straight to MP4, with system audio, microphone, and a webcam overlay, all on your device.
Frequently asked questions
Quick answers about converting WebM to MP4 here.
Is my video uploaded to a server?
No. The conversion runs entirely in your browser using ffmpeg compiled to WebAssembly. Your video is read from your device, converted on your device, and saved back to your device. Nothing is uploaded, and there is no account. That is the main difference from most "WebM to MP4" websites, which upload your file to their servers.
Do I need to install anything?
No. It is a normal web page - no app, no browser extension, and no admin rights. The first conversion downloads the ffmpeg engine (about 30 MB) to your browser cache, then it is ready immediately next time.
What formats can I convert from?
WebM is the main one, but it also reads common video files such as MOV, MKV, and AVI and converts them to MP4. The output is H.264 video with AAC audio, which is broadly compatible.
Is there a file size or length limit?
There is no hard limit, but because everything runs in your browser, very large or very long videos can be slow or run out of memory. For big files a shorter clip, or a desktop tool, is more reliable. Most screen recordings convert fine.
Why is it slower than a desktop converter?
Desktop converters use your computer's native video hardware. This runs ffmpeg inside the browser sandbox, which is slower but means your file never has to be uploaded anywhere. It is the trade-off for keeping the video private and needing no install.
Does the MP4 have a watermark?
No. There is no watermark, no signup, and no length cap added to the output. You get a clean MP4.
Can I just record straight to MP4 instead?
Yes. Our screen recorder can save recordings directly as MP4, so you can skip the conversion step entirely for anything you record from now on.