What is MKV?
Matroska Multimedia Container
MKV (or Matroska Multimedia Container) is a free, open source video container format created in 2002. It’s officially called Matroska after the Russian matryoshka dolls because all the video, audio, and subtitle tracks are held within a single file. This format enables synchronous playback of audio and video tracks. Since MKV supports a large number of codecs and even uncompressed video, this format retains the original quality, allowing you to enjoy your videos in HD. Check this table if you want to know how to open MKV files and which programs can play them.
.mkv, .mk3d, .mka, .mks
Videos with the MKV file type have a data channel for each type of track, making this format closer to other media containers such as AVI or MP4. A disadvantage of the MKV format is that very few modern programs can play files with these specifications correctly, so users have to install additional applications or codecs, for example, the VLC player or K-Lite Codec Pack.