WEBM Compressor
Compress WebM videos using VP9 with constant-quality encoding.
Drop or click to select (webm, mkv)
First run downloads ~30MB ffmpeg engine; subsequent runs are instant. Everything stays in your browser.
About this tool
WebM is the open-source video format championed by Google and Mozilla. It uses the VP8/VP9 (or now AV1) codec, which typically produces smaller files than H.264 at the same visual quality. WebM is the format of choice for embedding video on a website because it streams well and is supported by every modern browser.
This WebM Compressor uses ffmpeg compiled to WebAssembly to re-encode your file at a lower bitrate, locally in your browser. Your video is never uploaded to a server, so even sensitive material stays on your machine.
If you're producing video for the web, WebM at moderate compression often beats an MP4 of the same visual quality by 20% or more in file size.
Why use it
- 100% in-browser — no upload, no server, no signup.
- Powered by ffmpeg.wasm — the same engine pros use.
- Set a target file size in MB to hit upload limits exactly.
- Free with no watermark.
How to use it
- 1Drop a WebM clip
Add your .webm file via drag-and-drop or the file picker.
- 2Pick CRF or target size
Lower CRF for better quality and larger files, higher CRF for smaller files. Or set the target MB directly.
- 3Download the new WebM
When the encode finishes, your smaller WebM is ready to embed or share.
Common use cases
- Embedding short background videos on a landing page.
- Optimizing video assets for a website to improve performance.
- Reducing screen-recording WebMs from browser extensions.
- Preparing HTML5 video for online courses and documentation.
Tips for best results
The ffmpeg engine (~30 MB) downloads and caches the first time you use it. After that it stays ready for instant runs.
Dropping a 4K clip to 1080p often halves the file before you even touch the bitrate.
If only the first 30 seconds matter, cutting the rest of the clip is the cheapest way to shrink the file.