This will allow you to just type mplayer /path/to/file in the terminal
to launch it.
If you don't you'll have to type out the whole path to the binary.
/usr/local/bin/mplayer /path/to/file
MPlayer 1.3.0-4.2.1 (C) 2000-2016 MPlayer Team
224 audio & 451 video codecs
Usage: mplayer [options] filename
===============================================
New as of 01/09/2023: MPlayer launcher. I created a small app that you
can drop a video file on to and it will launch mplayer. You can also
associate video files with it to always open with MPlayer. It's a lot
nicer than using the command line.