Drop your WebM file. We'll convert it to MP4 right here in your browser, your file never leaves your device.
Drop your file here
or click to pick from your device
How it works
Click the dropzone above or drag a WebM from your desktop. Files of any size, there's no upload, so there's no upload limit.
The conversion runs entirely in this tab using JavaScript and WebAssembly. Your file never touches our servers, we don't have any.
Get your MP4 the moment the conversion finishes. Convert another, or close the tab.
Your file is never uploaded. The entire conversion runs in your browser using WebAssembly. We can't see what you convert because we have no server to see it.
Server converters cap free users at 1-2 GB and gate larger files behind a paid plan. Since nothing uploads, our limit is whatever your browser can handle.
No account required. No watermark on the output. No queue. Open source, every line of conversion code is public.
Formats involved
WebM is Google's open-source video container, designed for web streaming. Uses VP8/VP9 video and Vorbis/Opus audio. About 25-35% smaller than equivalent H.264 MP4 at the same quality. Universal browser support; less common on standalone media players and older hardware.
How to open
All modern web browsers, VLC, MPV. Some smart TVs and older players don't recognize WebM, converting to MP4 is the standard fix.
MP4 is the dominant video container on the web, H.264 video plus AAC audio, in a structure designed for streaming. Every browser, mobile device, smart TV, and editing tool reads MP4. The format is technically a container (not a codec), so two MP4 files can have very different internal codecs, but the H.264+AAC default is what enables universal playback.
How to open
Every video player on the planet, VLC, QuickTime, Windows Media Player, browsers (HTML5 video), iOS, Android, smart TVs, game consoles. Universal.
Related tools
How we compare
| Feature | Ustwineconvert | CloudConvert | iLovePDF | FreeConvert | Smallpdf |
|---|---|---|---|---|---|
| Files uploaded to a server | |||||
| Free file size limit | No limit | 1 GB | 200 MB | 1 GB | 5 GB |
| Free conversions per day | Unlimited | 10/day | Limited | Limited | 2/day |
| Signup required | |||||
| Watermark on output | |||||
| Open source | |||||
| Works offline (after first load) |
Last verified May 2026 from each competitor's pricing and FAQ pages. Limits and pricing change frequently.
FAQ
Yes. No signup, no watermark, no daily file count limit. The entire engine is open source, you can read the conversion code on GitHub.
Nowhere. The conversion runs entirely in your browser using JavaScript and WebAssembly. Your file is never uploaded to our servers. We don't have any servers handling files, there's nothing for us to log, store, or accidentally leak.
Whatever your browser can hold in memory. Practically, this means a few hundred MB on most computers, significantly larger than the 1-2 GB caps that server-upload converters charge for. Very large files (multi-GB) may require closing other browser tabs first.
Web video where smaller file size matters more than universal playback. Web video, mobile video recording, video sharing. The most common reason to convert is compatibility, MP4 works in places where WebM doesn't, or vice versa.
All modern web browsers, VLC, MPV. Some smart TVs and older players don't recognize WebM, converting to MP4 is the standard fix.
Once the page is loaded, the conversion itself runs entirely offline. The first time you use a tool, your browser downloads the conversion library (a one-time cache). If you reload while offline, the page won't load, but you can install the site as a Progressive Web App for full offline use.
Single file at a time for now. Batch conversion is on the roadmap, for now, drop one file, download the result, then convert the next.