Convert MP4 to WebM
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WebM is the format most web pages, HTML5 video players, and modern CMS platforms prefer — it usually compresses better than MP4 at the same quality and is the standard many sites ask for on upload. This tool takes your MP4 and re-encodes it into WebM using VP9 video and Opus audio.
The re-encode happens locally through your browser’s built-in WebCodecs support, so no part of your video is uploaded to convert it — the whole process stays on your machine, start to finish.
Also useful: Convert WebM to MP4 · Convert MP4 to MP3
How it works
- Upload the MP4 video file you want to convert to WebM.
- Wait while your browser re-encodes it into VP9/Opus using WebCodecs.
- Download your converted WebM file.
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Frequently asked questions
Why would I want WebM instead of MP4?
WebM (VP9/Opus) often produces smaller files at similar quality and is the format a lot of websites and video players are optimized for, especially open-source or privacy-focused platforms.
Is my MP4 file uploaded during conversion?
No — the entire encode runs client-side using the WebCodecs API. Your original MP4 and the WebM output both stay on your device.
What size, length, and browser do I need?
Up to 300MB on desktop (100MB on mobile), up to 30 minutes long on desktop (10 on mobile). Use an up-to-date Chrome, Edge, Firefox, or Safari, since the WebM encode relies on WebCodecs.