MKVToolnix is a set of tools to create, alter and inspect Matroska
files. With these tools one can get information about  (mkvinfo)
Matroska files, extract tracks/data from (mkvextract) Matroska
files and create (mkvmerge) Matroska files from other media files.
Matroska is a new multimedia file format aiming to become THE new 
container format for the future. 

Beyond dependencies already satisfied under Slackware MKVToolnix
requires libebml, libmatroska, wxGTK and the Boost regex library. 
All of these are available on Slackbuilds.org.