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MKV
What is an MKV file?
An open container that holds anything — several audio tracks, subtitles, chapters. Weak on hardware players.
What MKV is
MKV is a container: a wrapper that holds streams encoded by something else. It is used for archiving and handing a finished file over.
The extension is .mkv, and the full name is Matroska Video. Both matter less than what the file can hold, which is what the rest of this page is about.
Where MKV came from
It dates from 2002. The specification is Matroska.
Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.
The specification is public
Anyone can implement it without asking permission or paying a licence, which is why it turns up in so many programs and why files written twenty years ago still open.
MKV is a box, and the codec is what is in it
It usually holds H.264, HEVC, AV1, VP9 and FLAC. This is the distinction behind most "why will this not play" questions: two files with the same extension can contain entirely different encodings, and a player that refuses one may be perfectly happy with the other.
It also explains why changing container is often fast and lossless while changing codec is neither. Moving the same stream into a different box rewrites the box; re-encoding rewrites the picture.
What else it can carry
MKV can hold several audio tracks and subtitle tracks.
That matters mostly when converting: whatever the target cannot hold is dropped, usually without a warning.
What opens MKV
VLC, MKVToolNix and HandBrake read it, and so do most programs of the same kind.
If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.
Opening it in a browser
No browser reads it.
That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.
It is a delivery format
MKV is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.
What goes wrong with it
The recurring complaints: support outside its home ground is uneven.
None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.
The facts, in one place
| Extension | .mkv |
|---|---|
| Media type | video/x-matroska |
| First published | 2002 |
| Specification | Matroska |