MKV to WebM Converter
Runs in your browser — your files are never uploaded.
Convert a Matroska file to WebM for the open web. The two containers are closely related — WebM is a deliberately restricted subset of Matroska — but the codecs usually are not: an MKV typically carries H.264 or HEVC, and WebM allows only VP8/VP9 with Vorbis or Opus. That means a real re-encode rather than a repackage, which is why this takes time.
OptionsResolution: Original
How to convert MKV to WebM
- 1
Drop your .mkv file onto the box, or click to choose one.
- 2
OkConverter loads the engine once per session and re-encodes to VP8 with Opus audio.
- 3
Click “Download” to save the .webm file.
Share
Embed this tool on your site
Paste this where you want the tool to appear. It runs entirely in your visitor's browser — no uploads, no account, no tracking.
Please keep the attribution line — it's what keeps these tools free.
Need a different size, a dark theme, or a different tool? Build an embed lets you preview it first.
Frequently asked questions
WebM is basically MKV — why can it not just be renamed?+
Because WebM restricts which codecs are allowed inside the container. Renaming an MKV holding H.264 gives you a file that browsers refuse to play, since the codec is not permitted in WebM regardless of what the extension says. The video genuinely has to be re-encoded to VP8 or VP9.
Why is it slow?+
VP8 encoding runs single-threaded in WebAssembly, with no access to your GPU. A short clip is comfortable; a full-length video will take a long time. That is the cost of not uploading it anywhere.
What about subtitles inside the MKV?+
They are dropped. WebM supports only WebVTT tracks, and most MKV subtitles are SRT or ASS. Extract them separately and convert them with the subtitle tools if you need them.