3D stereoscopic file created in Matroska 3D format. The .MK3D format is essentially a .MKV file container that has a special field set defining what type of stereoscopic 3D video material is contained in the file.

The stereo 3D support for Matroska video files can be realized with either two separate video tracks - one for each eye, or with a single video track containing both the data for the left and right eye.