.mkv — Matroska Video
Video video/x-matroska
What a .mkv file is
An open container that can hold essentially any codec, plus multiple audio tracks, subtitles and chapters in one file.
How to open it
VLC, MPV, Plex. Browsers and phones generally will not play it directly.
Worth knowing
The format of choice for archiving, because it puts no constraints on what it carries.
How to identify a .mkv file
A file's extension is only its name — renaming a.png to a.mkv changes nothing inside. What software actually reads is the magic number, the first few bytes of the file.
| Signature | 1A 45 DF A3 |
| MIME type | video/x-matroska |
| Category | Video |
An EBML header — shared with WebM.
# what is this file really?
file mystery.mkv
# look at the first bytes yourself
xxd mystery.mkv | head -2
head -c 16 mystery.mkv | xxd
# Windows PowerShell
Get-Content mystery.mkv -AsByteStream -TotalCount 16 | Format-HexFrequently asked questions
What is a .mkv file?
An open container that can hold essentially any codec, plus multiple audio tracks, subtitles and chapters in one file.
How do I open a .mkv file?
VLC, MPV, Plex. Browsers and phones generally will not play it directly.
Is .mkv safe to open?
Yes. A .mkv file is data, not code — opening one cannot execute anything by itself.
Can I change a file's extension to convert it?
No. Renaming changes the label, not the bytes. The one place it appears to work is between formats that genuinely share a container — renaming .docx to .zip works because a DOCX is a ZIP. Everything else needs a real converter.