On your mac:

After installing mpv, confirm the folder ~/.config/mpv/ exists

We need to create a FIFO file for mpv to read commands from. To do so, execute the following in a terminal:

mkfifo ~/.config/mpv/fifo

Now we need to tell mpv to read from this file. Edit ~/.config/mpv/config and add the following line:

input-file=~/.config/mpv/fifo

Enable Remote Login in System Preferences > Sharing and take note of the IP address listed: