Convert video to WEBM
Convert MP4, MOV and other video files to WEBM with VP9 video and Opus audio, entirely in your browser. Smaller files for web delivery.
Your file is processed entirely in this browser tab. It is never uploaded, stored or seen by anyone.
To convert a video to WEBM, drop the file into the converter above and choose WEBM. The video is re-encoded to VP9 with Opus audio — an open, royalty-free combination that produces noticeably smaller files than H.264 at the same visual quality, at the cost of a slower encode.
How it works
- Choose your file
Drag a file onto the converter, or click to browse. Nothing is uploaded — the file is read directly by your browser.
- Convert to WEBM
Press Convert. FFmpeg runs as WebAssembly inside the tab and shows real progress as it works.
- Download the result
When it finishes, download the WEBM file. It is created in your browser's memory and never sent anywhere.
Your file never leaves your device — conversion runs entirely in this browser tab.
About WEBM
WEBM pairs VP9 video with Opus audio in a Matroska-derived container. Both codecs are open and royalty-free, which is why Google adopted them for YouTube delivery and why they are the default choice for self-hosted web video where H.264 licensing is a concern.
The practical argument for WEBM is size. VP9 typically delivers the same perceived quality as H.264 in 30–50% fewer bits, which is significant if you are paying for bandwidth on a video that loads on every page view. The practical argument against it is encode time — VP9 is substantially slower to encode, and in a browser that penalty compounds with the WebAssembly overhead.
Expect a WEBM conversion to take considerably longer than the equivalent MP4. For a hero video encoded once and served a million times, that trade is obviously worth it. For a one-off file you need to send someone, MP4 is the better answer.
| Codec | VP9 + Opus |
|---|---|
| Container | WebM (Matroska subset) |
| Typical bitrate | 1–12 Mbps at 1080p |
| Compatibility | All modern browsers; poor on older Safari and most TVs |
| Best for | Self-hosted web video, background loops, bandwidth saving |
Limits you should know about
Because conversion happens on your device rather than on a server, the ceiling is your browser's memory rather than our disk space. Files under 50MB work reliably everywhere. Desktop browsers stretch to roughly 200MB; mobile browsers, and iOS Safari in particular, cut out closer to 40MB.
Speed is the other trade. Running FFmpeg through WebAssembly is 5–10× slower than a desktop app, so a conversion that takes thirty seconds in a desktop application can take several minutes here. The converter shows a real estimate before it starts, and the tab has to stay open while it runs.
If your file is beyond those limits, trim it first, or use a desktop application such as HandBrake or FFmpeg directly — neither has a size ceiling.
Common questions
Is WEBM better than MP4?
For web delivery, usually — VP9 achieves similar quality in 30–50% fewer bits. For compatibility, no. WEBM fails on older Safari versions, most smart TVs, and many video editors. Serve WEBM with an MP4 fallback if you need both.
Why does WEBM conversion take so long?
VP9 is a much more computationally expensive encoder than H.264, and running it through WebAssembly adds a further 5–10× penalty. A file that converts to MP4 in two minutes may take ten as WEBM.
Can I upload WEBM to YouTube?
Yes, YouTube accepts WEBM. But it re-encodes everything on upload anyway, so there is no quality advantage — and MP4 uploads faster from most connections.