What is this MKV to WebM converter?
A free, browser-based tool that converts a MKV video to WebM. Add a file, preview it inline, and download the result. All processing happens locally in your browser, so your video is never uploaded and there is no watermark.
OBS records MKV; your website wants WebM
OBS defaults to MKV for a good reason: if the app or the machine dies mid-session, the recording up to that point still opens. That crash-safety makes MKV the right capture format for demos, streams, and screencasts, and the wrong format for the web, where browsers expect WebM or MP4 inside a <video> tag.
Converting the capture to WebM closes that gap: the product demo goes on the landing page, the stream highlight into the docs, playing natively in every modern browser.
H.264 captures re-encode; AV1 and VP9 captures remux
Most OBS setups record H.264 through x264 or NVENC, and WebM cannot carry H.264, so those files go through a full re-encode into a WebM-compatible codec. That takes time on long recordings and puts the quality choice in your hands. There is a silver lining: OBS recording bitrates are generous by web standards, and the re-encode is where a bulky capture becomes a page-appropriate file.
If you record with the newer AV1 encoders (or in VP9), the story flips: WebM accepts those streams directly, so the conversion is an instant remux with the picture untouched. A quick look at the encoder setting in OBS before your next long session tells you which path lies ahead.
How to use it
- Add a MKV file on the left (drag & drop or click) — it shows an inline preview.
- Pick a quality preset (used only when the video has to be re-encoded).
- Press “Convert & download” to get your WebM file. The first run downloads the ~30MB converter once.
Lossless remux vs re-encoding
MKV and WebM are containers — what matters is the video codec inside. When the codec already fits WebM, this tool just repackages it (a "remux"): instant and completely lossless. Only when the codec isn't compatible — most often anything involving WebM — does it re-encode the video locally, which takes longer and is where the quality preset applies.