Add your WEBM file
Drop one or more .webm files onto the converter above, or browse for them. They load into browser memory only — nothing is uploaded, so there is no size-based pricing and no server queue.
WEBM to MKV
Converting .webm video to .mkv means re-encoding the picture and sound into a different container and codec family, and this page does it entirely in your browser. Free, private, and validated — the file never leaves your browser.
100% private for supported formats
Runs on your deviceConvert supported files
Drop WEBM files here
Batch files can each use a different output. Nothing uploads for local conversions.
Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.About converting WebM video to Matroska video
Converting .webm video to .mkv means re-encoding the picture and sound into a different container and codec family, and this page does it entirely in your browser. A .webm file is an open, royalty-free video container built specifically for the web. It restricts itself to free codecs, VP8, VP9, or AV1 for video with Vorbis or Opus for audio, so any browser can play a .webm without patent licensing concerns.
An .mkv file uses the Matroska container, an open format designed to hold an unlimited number of video, audio, and subtitle tracks in one file. Collectors of high-quality rips and archival copies favor .mkv because it keeps every language track, chapter marker, and font attachment together. For this route the practical draw is holds essentially any combination of codecs and track types and fully open and royalty-free specification — balanced against safari and iOS refuse the container outright, which is worth knowing before you commit a large batch.
Why convert WEBM to MKV?
The practical trigger for this conversion is usually a mismatch: with .webm, older iPhones and legacy Safari versions cannot play it. Switching to .mkv buys you holds essentially any combination of codecs and track types, which is why it is the better fit for archiving discs while preserving every audio track and subtitle stream. Because the conversion runs locally, trying it costs nothing but a few seconds of compute on your own machine.
WEBM vs MKV at a glance
| Aspect | WebM video (.webm) | Matroska video (.mkv) |
|---|---|---|
| Format type | Container — quality depends on the codecs and settings inside | Container — quality depends on the codecs and settings inside |
| How it stores data | structured as a deliberately restricted subset of Matroska's EBML layout | built on EBML, a binary XML-like structure that lets the container gain features without breaking older parsers |
| Strongest at | serving HTML5 video without codec license fees | archiving discs while preserving every audio track and subtitle stream |
| Weak spot | older iPhones and legacy Safari versions cannot play it | safari and iOS refuse the container outright |
| Metadata | only a minimal set of Matroska tags such as title and language is defined for WebM; the spec deliberately omits attachments and rich tagging | matroska tags cover title, cast, and arbitrary key-value pairs, and the container can embed cover art and other files as attachments |
Pick MKV as the output
Select .mkv in the output menu next to each file. The menu only offers targets this engine can genuinely produce, so if MKV is selectable, the route is real and validated.
Convert on your device
Press Convert. The conversion runs on an FFmpeg engine compiled to WebAssembly, executing entirely inside your browser tab.
Verify and download
Each result is signature-checked before the download unlocks, so a failed encode can never masquerade as a valid MKV file. Outputs keep the original filename with the .mkv extension.
WEBM to MKV questions, answered
Will converting WEBM to MKV lose quality?
Both sides are re-encoded, so expect a small generation loss controlled by the quality setting: webm is container-oriented and mkv is container-oriented. For visually or audibly transparent results keep quality high; for smaller files lower it and compare.
Is it private to convert WEBM files here?
Yes — the .webm file is processed inside your browser tab and never uploaded. The conversion runs on an FFmpeg engine compiled to WebAssembly, executing entirely inside your browser tab. Close the tab and the file is gone from memory.
Where will the MKV file work?
Chrome, Firefox, and Edge can play Matroska files whose codecs they support, but Safari rejects the container on both macOS and iOS. VLC, mpv, and Plex handle .mkv everywhere, and Windows has shipped native Matroska playback since Windows 10.
Will the MKV file be bigger or smaller than my WEBM?
It depends on the content: built on EBML, a binary XML-like structure that lets the container gain features without breaking older parsers. Convert one representative file first and compare before batch-processing a large set.
What happens to the metadata in my WEBM file?
This converter strips container metadata deliberately (the FFmpeg command runs with metadata mapping disabled) so exported files do not leak recording details. In the source, only a minimal set of Matroska tags such as title and language is defined for WebM; the spec deliberately omits attachments and rich tagging; none of it is transmitted anywhere because the file never leaves your browser.
Can I convert MKV back to WEBM?
Yes — the reverse route exists as a separate tool. Bear in mind that round-tripping .webm → .mkv → .webm is not a perfect undo when any lossy step is involved; keep your original if fidelity matters.