About this tool
WebM is the open format some websites, wikis, and open-source projects require for embedded video. This converter re-encodes MP4 (H.264) to VP8 video with Vorbis audio, which every modern browser plays natively.
About the formats: MP4 is the universal video container, usually holding H.264 video and AAC audio. It plays on every phone, browser, TV, and editing program, which is why most platforms ask for it. WebM is the open web video container (VP8, VP9, or AV1 video with Opus or Vorbis audio) produced by browser-based screen recorders and Chrome extensions. It works well in browsers, but iPhones, TVs, and most editing software will not open it.
Everything happens inside your browser. Your file is never uploaded to a server: the conversion runs on your own device using WebAssembly, and the result is downloaded straight from memory. Close the tab and nothing is left behind.
How to use it
- Drop your MP4 files into the box above, or click to browse. Nothing is uploaded.
- Click Convert to WEBM and wait a moment.
- Download the results individually or all at once as a ZIP.
Frequently asked questions
Why does MP4 to WebM take a while?
VP8 encoding is CPU-heavy and runs on one core in the browser. Short clips take a minute or two; long videos can take much longer.
Does WebM play on iPhone?
Safari on iOS 15 and later plays WebM in the browser, but the Photos app does not. Use MP4 for sharing with iPhone users.
Is this really free?
Yes. The site is supported by ads, and there are no limits on how many files you convert.
Are my files uploaded anywhere?
No. The converter runs entirely in your browser. Files stay on your device, which also makes it faster than upload-based converters for anything larger than a few megabytes.
Is there a file size limit?
The only limit is your device's memory. Images and audio of any normal size are fine; for video, files under about 500 MB work well on most laptops and phones.
Which browsers are supported?
Current versions of Chrome, Edge, Firefox, and Safari on desktop and mobile. Very old browsers without WebAssembly support will not work.