The MSP protocol definition can be found at: https://www.zuggsoft.com/zmud/msp.htm

MSP are completely inline commands for instructing the client to play sound media.

Command Format:

!!MUSIC(filename V=volume L=repeats C=continue T=url P=priority)
!!SOUND(filename V=volume L=repeats C=continue T=url P=priority)

MSP is extremely simple. The filename is the name of the sound file, e.g. "sound.wav", while volume and priority are numbers from 0-100. Continue (not supported here) is 0 or 1, while the url is the web location that the sound can be downloaded fromm, e.g. "http://coffeemud.net/sounds/". If the filename is the word "off", then it will stop playing.