MKV

MKV refers to the Matroska multimedia container format, when used for video. It can use a variety of compressed video formats.

Software
See also Matroska.
 * Konvertor
 * VLC
 * FFmpeg

Sample files

 * http://www.matroska.org/downloads/test_w1.html
 * http://www.auby.no/files/video_tests/
 * Matroska.
 * https://telparia.com/fileFormatSamples/video/mkv/