Convert MP4 to WebM
Convert MP4 to WebM by dropping a video under 50MB onto this page and clicking the button; the WebM downloads when the in-browser encode finishes. ffmpeg compiled to WebAssembly does the work locally, so the clip is never uploaded.
Drop your MP4 here
It becomes a WebM right in your browser, up to 50 MB
Your file never leaves your device
Why convert MP4 to WebM?
WebM exists for the open web: royalty-free codecs, first-class HTML5 video support, and a license story that never sends lawyers after your embedded player. Converting an MP4 to WebM suits clips headed into web pages, open-source projects, federated platforms and anywhere the patent-encumbered H.264 stack is unwelcome. Some platforms also prefer or auto-convert to WebM, so arriving in the right format skips a re-encode you do not control. This pair is scoped honestly: it is built for short, small clips like screen recordings and product demos, not feature films, because a browser tab has one CPU's worth of patience.
What is MP4?
MP4 is the default container of modern video: phones record into it, cameras export it, and every browser, TV and editing tool plays it, usually carrying H.264 video and AAC audio. Being a container, an MP4 is really a box around separate video and audio tracks, which is why useful conversions include not just other video formats but also pulling the audio track out on its own.
What is WebM?
WebM is the web-native, royalty-free video format Google introduced in 2010, built on the VP8/VP9 video codecs and Vorbis or Opus audio. Every modern browser plays WebM directly, HTML5 video embraces it, and no patent licensing is attached to it anywhere in the chain. Outside browsers it is less at home: many desktop players, editing suites and devices still prefer MP4.
Quality and what to expect
Video transcoding is the most demanding thing this site does, and the settings reflect a deliberate trade: the VP8 encoder runs in its faster mode so that conversions finish in minutes rather than hours, which costs some compression efficiency against a slow studio-grade encode. For screen recordings, demos and short clips the output looks clean; bit-starved fast action will show it first. Audio is re-encoded to Vorbis. Expect roughly real-time to 3x real-time encoding depending on resolution and your CPU. Files over 50MB are politely refused rather than left to grind; a server engine for big video is coming.
MP4 to WebM FAQ
Why is there a 50MB limit on this conversion?
Encoding video in WebAssembly runs on a single browser thread, so time grows with every megabyte. We measured where the experience stops being reasonable and drew the line at 50MB; beyond it, the job belongs on a server engine, which is on the roadmap.
How long will my conversion take?
Rough rule: about as long as the clip itself, sometimes up to a few times longer for high-resolution sources. A 30-second screen recording finishes quickly; a 10MB clip typically completes within a minute or two.
Is the video uploaded while it converts?
No. The encoder, the input and the output all live inside your browser tab. You can disconnect from the internet after the page loads and the conversion will still complete, which is a stronger proof than any privacy policy.
Will the WebM play everywhere my MP4 did?
In browsers, yes, universally. Outside browsers, MP4 still has the edge: some TVs, older players and editing tools handle WebM poorly. Keep the MP4 for those contexts and serve the WebM on the web.