A quick-and-easy AppleScript to 1) loop a background music file, and 2) fade that file out when a dialog button is pressed. I use this when presenting slide decks virtually.

Background Music.applescript

tell application "QuickTime Player"
	set theFile to open POSIX file "FILENAME HERE"
	set audio volume of theFile to 0.3
	set looping of theFile to true
	play theFile
	
end tell
display dialog "Music Control" buttons {"Fade"}

tell application "QuickTime Player"
	repeat 30 times
		set theValue to (audio volume of theFile) - 0.01
		set audio volume of theFile to theValue
		delay 0.2
	end repeat
	quit
end tell