MKV File Format (.mkv)
An MKV file is a Matroska container built on the EBML binary format, and it can hold any number of video, audio, subtitle and attachment tracks, encoded with essentially any codec, in a single file.
MKV at a glance#
| Full name | Matroska Video |
|---|---|
| File extension | .mkv |
| Category | Video Files |
| Developer | Matroska (Steve Lhomme and contributors) |
| First released | 2002 |
| MIME types | video/matroskavideo/x-matroska |
| Compression | Varies from file to file |
| Specification | RFC 9559 (Matroska Media Container Format Specification) |
| FileFlip support | FileFlip reads and writes this format |
What a .mkv file can hold#
These are the things a MKV file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.
| Embedded metadata | Yes |
|---|---|
| Colour profiles | Yes |
| High dynamic range | Yes |
| Audio | Yes |
| Video | Yes |
| Subtitle tracks | Yes |
| Chapters | Yes |
| Encryption | No |
| Streaming | Yes |
Strengths and limitations of MKV#
What MKV does well
- No fixed limit on file size, number of tracks, or which codecs those tracks use, unlike MP4 or AVI
- Holds multiple subtitle tracks in formats like ASS and PGS, plus font attachments to render them correctly, in the one file
- An open, royalty-free specification now published as IETF RFC 9559, so no licensing question attaches to the container itself
- The basis WebM was defined from, so anything that can parse Matroska is most of the way to parsing WebM too
Where MKV falls short
- Many smart TVs, game consoles and streaming boxes never implemented an MKV demuxer at all, even when they can decode the exact same codec inside an MP4
- Apple's own software, QuickTime, Photos and the Apple TV app, has no native MKV support
- No widely adopted DRM standard exists for Matroska, which is why commercial streaming services don't deliver video in it
Use MKV when a video needs multiple audio tracks, several subtitle languages, or a codec MP4 doesn't accommodate, and it's staying on software you control, like a media server or a desktop player.
Convert MKV to MP4 when a file needs to play on a device that never added MKV support, since that's usually a hardware or software gap rather than anything wrong with the codec inside.
How to open a .mkv file#
A .mkv file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts MKV into a format your machine already opens, and it does it in the browser tab rather than on a server.
| Platform | Programs that open it |
|---|---|
| Windows | VLC, MPC-HC |
| macOS | VLC, IINA |
| Linux | VLC, mpv |
| iOS | VLC, Infuse |
| Android | VLC, MX Player |
| Web | FileFlip |
MKV questions people ask#
Why won't my TV or game console play an MKV file?
MKV is just a container, so the refusal is almost always about the container itself rather than the codec inside it. A lot of hardware players, smart TVs, the PS5, some streaming boxes, never implemented support for parsing Matroska, even though they can decode the exact same H.264 or H.265 video when it's wrapped in an MP4.
Is MKV a video codec?
No, MKV is Matroska, a container format, not a codec. It doesn't encode video itself; it just holds whatever video, audio and subtitle tracks were put into it, which can use nearly any codec that exists.
Should I use MKV or MP4?
MP4 wins on compatibility, since it plays almost anywhere. MKV wins on flexibility, holding multiple audio and subtitle tracks, chapters and font attachments that MP4 either can't carry or supports less completely. Pick MKV for archiving or editing where you control playback, and MP4 for anything that needs to just work on an unfamiliar device.
Does converting MKV to MP4 lose quality?
Only if the codecs inside need to change. When an MKV already holds H.264 or H.265 video with AAC audio, moving it to MP4 is a remux, repackaging the same compressed data with nothing re-encoded and no quality lost. A subtitle track in ASS or PGS format has no direct equivalent in MP4 though, so that part either gets converted to a compatible format or dropped.
Can MKV files be streamed or does everything have to download first?
Matroska was designed with streaming in mind, with an index that lets a player seek and start playback without the whole file being present. In practice almost no commercial streaming service delivers video in MKV, since there's no DRM standard for it that content owners have adopted.
Converting MKV files#
Convert MKV to another format
Convert another format to MKV
Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.