MKV is a container format for holding multiple audio, video, picture, and text data such as subtitle tracks. It is similar to other common containers like MP4 and AVI, although MKV is open in the specification. For video contents, MKV uses a .mkv filename extension, .mka for audios, and .mks for subtitles.
MPC-HC, KMPlayer VLC Media Player MKV File Player MPV
OGV is a digital video container format related to the encoding technology of the OGG Vorbis video. It can save multiple related video stream codecs like the DivX and Theora. It is these codecs that allow OGV files to open on varying media players.
MPLayer Classic VLC Media Player Jriver Media Center MPUI