MK3D

MK3D is a version of the MKV (Matroska) video container format designed for 3D video, with a special field to designate the 3D video type used.

Software
See also Matroska.
 * Konvertor

Sample files

 * https://samples.ffmpeg.org/stereo3d/ → *.mk3d

Links

 * Some format info
 * Some discussion