I have configured Volumio (3.179 on RPi4) for the OSMC remote control.
here is my /etc/triggerhappy/tiggers.d/audio.conf
#VOLUMIO TRIGGERHAPPY CONFIGURATION FILE
#MUTE TOGGLE
KEY_ENTER 1 /usr/local/bin/volumio volume toggle
#VOLUME UP
KEY_EQUAL 1 /usr/local/bin/volumio volume plus
KEY_EQUAL 2 /usr/local/bin/volumio volume plus
#VOLUME DOWN
KEY_MINUS 1 /usr/local/bin/volumio volume minus
KEY_MINUS 2 /usr/local/bin/volumio volume minus
#PLAY PAUSE TOGGLE
KEY_PLAYPAUSE 1 /usr/local/bin/volumio toggle
#STOP
KEY_STOP 1 /usr/local/bin/volumio stop
#CLEAR
KEY_ESC 1 /usr/local/bin/volumio clear
#NEXT
KEY_RIGHT 1 /usr/local/bin/volumio next
#PREVIOUS
KEY_LEFT 1 /usr/local/bin/volumio previous
#SEEK FORWARD
KEY_UP 1 /usr/local/bin/volumio seek plus
#SEEK BACKWARD
KEY_DOWN 1 /usr/local/bin/volumio seek minus
#REPEAT
KEY_C 1 /usr/local/bin/volumio repeat
#RANDOM
KEY_I 1 /usr/local/bin/volumio random
A couple of points I learned that are not in this thread:
to restart the service in V3 you need to run:
sudo systemctl restart triggerhappy
Not all events are on event0 so if you want to see all the button codes you need to run
sudo thd --dump /dev/input/event*
The volume control uses the step defied in the regular settings menu. If you use my config you should set the stepsize to 1 so that a single click on the volume up or down changes the volume by one increment, but pressing and holding gives a smooth increase or decrease for as long as it is held.