Convert WebM to Matroska (MKV)
Free online converter for WebM files. Flexible container for high-quality video. Nothing to install, no watermark, and every file is deleted automatically.
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Upload a WebM file to convert it to Matroska (MKV). Up to 3 files at once, 100 MB each.
Free · up to 3 files · 100 MB each · files deleted automatically after 1 hour.
About WEBM and MKV
WebM .webm
An open container built for the web, holding VP8, VP9 or AV1 video with Vorbis or Opus audio. Royalty-free by design.
Good for
- Open and royalty-free
- Smaller than H.264 MP4 at similar quality
- Supports transparency, which MP4 does not
Trade-offs
- Weaker support in desktop editors and older devices
- Slower to encode than H.264
- Not the safe choice for sending a file to someone
video/webm
Matroska (MKV) .mkv
Matroska: an open container that will hold almost any combination of video, audio, subtitle and chapter tracks in one file.
Good for
- Unlimited tracks — multiple languages, subtitles, chapters
- Codec-agnostic, so it holds nearly anything
- Open, well documented, and resilient to damage
Trade-offs
- Browsers will not play it natively
- Many TVs and phones refuse it — the usual reason to convert
- Being a container, contents vary wildly file to file
video/x-matroska
WEBM and MKV side by side
| WEBM | MKV | |
|---|---|---|
| Compression | Lossy (VP9 or AV1) | Container — any codec |
| Transparency | Yes — with VP9 or AV1 | Depends on codec |
| Typically used for | Web video, background loops with transparency | Archival video, multi-language releases |
What changes when you convert WEBM to MKV
WEBM and MKV are close relatives
WebM is Matroska with the guest list shortened: the same underlying container design as MKV, restricted to a deliberately narrow set of codecs. That is why the same player usually opens both, and it is worth knowing generally: the extension on a video tells you far less about it than the codec stored inside does.
This is a re-encode, not a repackage
Some tools can move a stream into a different container untouched when the codecs happen to line up. We do not — every job here is decoded and encoded again, so the conversion takes time in proportion to the length of the file and costs a small amount of quality even where a repackage would have been possible. In exchange the output is predictable: it plays everywhere, rather than inheriting whatever the source happened to contain.
What your MKV will contain
The output is H.264 video with AAC audio — Matroska imposes no codec restrictions, so the choice here is for compatibility rather than because the container demands it. What Matroska adds is room — multiple audio tracks, subtitles and chapters all have a proper place in it, which is why it is the format of choice for archiving a film.
Other WebM conversions
Other ways to get Matroska (MKV)
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