MKS is a filename extension associated with Matroska multimedia container format. MKS files store only subtitle streams, not audio or video data. MKS files are commonly used along MKV video files.

MKS is a popular and widely-used extension. The format allows importing subtitle data from such popular formats as SRT or SUB. MKS subtitles can also be exported to said formats in order to use them in programs that don’t support Matroska format.