MP4 to WebM Converter
Convert MP4 videos to efficient WebM (VP9 + Opus) for the web, in your browser. Free, private, no signup or upload.
About the MP4 to WebM Converter
This free MP4 to WebM converter re-encodes your MP4 into WebM using the modern VP9 video codec and Opus audio. WebM is the open, efficient format built for the web — smaller downloads at the same quality and native support in all modern browsers, ideal for background videos and HTML5 players.
The conversion runs entirely in your browser through FFmpeg WebAssembly, so your video is never uploaded. The engine (about 30 MB) downloads from a CDN on first use and is cached, so the first conversion is the slow one.
An honest note: VP9 is more computationally intensive than H.264 and runs single-threaded in the browser, so encoding is noticeably slower — be patient with longer clips. The payoff is an efficient, web-ready file. Videos up to 100 MB are supported.
How to Use the MP4 to WebM Converter
- 1Choose an MP4 file, up to 100 MB.
- 2Pick a quality — Balanced is recommended.
- 3Click Convert to WebM and wait for the progress bar (VP9 encoding is slower).
- 4Preview the WebM and download it.
Frequently Asked Questions
Is my file uploaded to a server?
No. All processing runs in your browser using FFmpeg compiled to WebAssembly. Your file never leaves your device — only the converter engine is downloaded, once.
Why is the first run slow?
The first time you use any converter here, the browser downloads the FFmpeg core (about 30 MB) from a CDN and compiles it. It is then cached for the session, so later runs are much faster.
Why is WebM conversion slow?
WebM uses the VP9 codec, which is far more demanding to encode than H.264 — especially single-threaded in the browser. It produces efficient files but takes longer, so expect a slower run than an MP4 conversion.
Why choose WebM?
WebM (VP9 + Opus) is open, royalty-free and very efficient, with native support in modern browsers. It is a great choice for websites, HTML5 video and background clips where small size matters.
Is there a file size limit?
Yes, 100 MB per file. Because everything runs in your browser's memory, very large files can be slow or run out of memory. Trim long clips first if you hit the limit.