MP4 to WebM Converter
Runs in your browser — your files are never uploaded.
Convert MP4 video to WebM, the open royalty-free format built for the web. Handy for HTML5 video where you want a patent-free alternative alongside your MP4, and for sites and wikis that only accept WebM uploads. The whole encode runs on your device using a real build of ffmpeg.
OptionsResolution: Original
How to convert MP4 to WebM
- 1
Drop your .mp4 file onto the box, or click to choose one.
- 2
OkConverter loads the conversion engine (one-time per session) and encodes VP8 video with Opus audio.
- 3
Click “Download” to save the .webm file.
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Frequently asked questions
Why does this take so long?+
WebM cannot reuse the MP4’s existing H.264 video, so every frame has to be re-encoded — and that runs single-threaded in your browser rather than on a server. A short clip is fine; a long high-resolution video will take a while. Leave the tab open and in the foreground.
Does it use VP8 or VP9?+
VP8, with Opus audio. VP9 compresses better on paper, but its encoder is not stable in the in-browser build of ffmpeg — it crashes partway through. VP8 produces a valid WebM that every browser plays.
Will the file be smaller than the MP4?+
Not necessarily, and often slightly larger. Modern H.264 is already efficient. Convert for the open format and browser compatibility, not to save space.
What size video is realistic?+
Short clips up to a minute or two at 720p convert comfortably. There is a 300MB input cap, but the practical limit is your patience and your device’s memory.
Is my video uploaded anywhere?+
No. Once the engine has loaded, the entire encode happens inside your browser tab.