MKVToolNix 19: MKVToolNix is a free application for editing MKV files.
With the free application you can cut a large file into smaller pieces, or vice versa join smaller pieces into a larger one. You can save the MKV audio to Mp3 and also easily integrate subtitles.
It is a very practical tool for those who have HD movies on their computer and want to edit them. 
MKVToolnix project developer Moritz Bunkus has announced the release of the new MKVToolnix 19.0.0. It is a bug fix release of the open-source and cross-platform (Windows, Linux and Unix) MKV (Matroska) application.
MKVToolNix 19.0.0 was released exactly one month after MKVToolNix 18.0.0 “Duel with the Devil” was released, and it seems to add a lot of new features and improvements, along with several bug fixes and some system changes.
The new MKVToolnix 19.0.0 comes with a new much more practical GUI that supports editing video color attributes. Version 19 is the last update for 2017.
You can see all the changes from the release notes and of course
download the application on the platform of your choice
