MP4 to WebM
Convert MP4 (or any video) to WebM (VP9 + Opus) for the web, entirely in your browser via ffmpeg.wasm.
WebM with VP9 video and Opus audio delivers smaller files than H.264 MP4 at comparable quality, which is why many web platforms prefer it for embedded video. This tool re-encodes MP4 (or most other video containers your browser can decode) into WebM using FFmpeg compiled to WebAssembly, running the entire conversion locally without an upload. VP9 encoding is computationally heavier than H.264, so expect it to take noticeably longer than the source video's runtime, especially for longer clips.
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How it works
- 01
Drop or select your MP4 or other video file.
- 02
Click Convert to re-encode with VP9 video and Opus audio.
- 03
Download the resulting WebM file.
Details
- Category
- Video
- Runs
- In your browser
- Files uploaded
- No
- Cost per run
- Free
- Sign-in
- Not required
- Works offline
- Yes, once loaded
Last updated 2026-08-03
Common questions
How long does conversion take?
VP9 encoding is slower than H.264 - expect it to take longer than the video's actual length, especially for longer clips.
Does it upload my video?
No - conversion runs locally with WebAssembly. Nothing leaves your browser.
Why choose WebM over MP4 for the web?
WebM/VP9 typically produces smaller files at similar visual quality, which improves page load times for embedded video.
Will WebM play in every browser?
All major modern browsers support WebM playback. For guaranteed support on very old browsers or devices, keep an MP4 fallback.