What is MKV Format ?
A file with the .MKV file extension is a Matroska Video file. It's a video container much like MOV and AVI, but also supports an unlimited number of audio, picture and subtitle tracks (like SRT or USF).
This format is often seen as the carrier for high-definition online video because it supports descriptions, ratings, cover art, and even chapter points — which is why MKV was chosen as the default video container format for the popular DivX Plus software
How to Play MKV Files Opening MKV files might sound like an easy task — just double-click it, like any other video file — but if you have a collection of 10 videos you got from 10 different places, you'll likely find that at least a few of those videos won't play correctly. This problem arises because the correct codecs for that particular type of video must already be present on your computer before the video stream will render. (More about codecs, below.) Your best bet for playing most MKV files is to use VLC. If you're on Windows, some other MKV players include MPV, MPC-HC, KMPlayer, DivX Player, MKV File Player or The Core Media Player. Some of those applications will open an MKV file on macOS, too, as can Elmedia Player. Though not free, Roxio software can be used to play MKV files on macOS as well. On Linux, open MKV files using xine and some of the programs above that work with Windows and Mac, like VLC. Play MKV files on iPhones, iPads, and iPods with the free PlayerXtreme Media Player or VLC for Mobile apps. VLC works with Android devices as well, as does Simple MP4 Video Player (it's named as such because MP4s and other video formats are supported). Use the CorePlayer mobile software to open MKV files on Palm, Symbian, Windows Mobile, and BlackBerry devices. However, the software is not free. Since you might need different programs to open different MKV files, you can always change the default program for a specific file extension in Windows. This step becomes necessary if, for example, KMPlayer is trying to open an MKV file that you instead want or need to use with DivX Player.