MKVToolNix is a set of cross-platform tools to create, alter, and inspect Matroska (MKV) files. Mkvmerge program takes the input from several media files and joins their streams (all of them or just a selection) into an MKV video file. Mkvinfo shows information about elements in an MKV file. Mkvextract can extract tracks from a file, and Mkvpropedit can modify properties of existing Matroska files without a complete remux. GUI for mkvmerge, called MMG is also included in the package.