MKV is a container format, a kind of Matroska media files, Matroska is a new multimedia package format, also known as multi-media containers (Multimedia Container). It can be a variety of encoded video and more than 16 different formats of audio and subtitle streams in different languages package them into a Matroska Media files. MKV to accommodate the greatest feature is the many different types of encoded video, audio and subtitle streams.
Free MKV player use the MPlayer as a standalone tool, it is a free and open source media player distributed under the GNU General Public License.