Mac users interested in Mkvtoolnix 4 generally download:
Create, edit, and play Matroska video files (MKV) on your Mac. Use a common way or the command-line to access the application, select files, modify them, edit tags, and chapters. Adjust the aspect ratio, display width and height, FPS, and other parameters.
Additional suggestions for Mkvtoolnix 4 by our robot:
Batch GUI for mkvpropedit (part of MKVToolNix) written in Java.
(part of MKVToolNix)