The latest version of MKVToolNix can be downloaded from Softpedia
MKVToolNix 6.4.1, a set of tools to create, alter, and inspect Matroska files under Linux and other platforms, has been released and it's ready for download.According to the developer, a few new features have been implemented, such as the ability to extract Opus tracks into OggOpus files or final Opus muxing.
Also, support has been added for the new Matroska elements DiscardPadding, CodecDelay and SeekPreRoll, libMatroska 1.4.1 is now required for building, a packet ordering regression has been corrected, and various other fixes and improvements have been added.
A complete changelog can be found in the official announcement. With MKVToolNix, users can get information about (mkvinfo) Matroska files, extract tracks/data from (mkvextract) Matroska files, and create (mkvmerge) Matroska files from other media files.
Download MKVToolNix 6.4.1 right now from Softpedia.