Convert MKV to WebM Online — No Upload, No Watermark
MKV is great for desktop playback but blocked by every modern browser and most CMSs. WebM is the open container browsers actually accept.
Drag & drop your video here, or click to browse
Max file size: ~2 GB (memory permitting)
Where MKV files come from
Both are open containers, so this is usually about getting a downloaded or recorded MKV onto a web page as a small, self-hosted asset.
What changes when you convert MKV to WebM
| Container | Matroska rewritten as WebM, a restricted subset of the same design |
|---|---|
| Video | H.264 or HEVC re-encoded to VP9 |
| Audio | Re-encoded to Opus |
Worth knowing first
WebM is deliberately a narrow subset of Matroska: only VP8, VP9 or AV1 for video and only Vorbis or Opus for audio. Everything else in the MKV, including extra audio tracks and subtitles, is dropped rather than carried across.
FAQ
If WebM is Matroska, why does it need re-encoding?
WebM is Matroska with a strict codec allowlist, created so browsers could support one predictable profile. An MKV holding H.264 is valid Matroska but not valid WebM, so the video genuinely has to be re-encoded rather than rewrapped.
Is this slow?
Yes. VP9 encoding is the expensive part and it runs on your processor here. Trim first if you only need part of the file.
What happens to subtitles?
They are dropped. For web playback, export them to WebVTT and attach a track element to your video, which is better for accessibility and search than burning them in.
Is this MKV to WebM converter really free and without upload?
Yes. The tool runs entirely in your browser using FFmpeg compiled to WebAssembly. Your MKV file never leaves your device — open the DevTools Network tab to verify zero uploads. No signup and no watermark. The practical size limit is the memory your browser gives this tab, which is generous on a computer and a few hundred megabytes on a phone.