MKVToolnix is a software that allows users to create, edit, and inspect Matroska (MKV) files. It offers a variety of features, including the ability to split and merge MKV files, extract audio and video tracks, and add or remove subtitles. The latest version (46.0.0) includes improved support for HEVC/H.265 video and Opus audio, as well as various bug fixes and improvements.