Starttrackvar
starttrackvar <track#>
starttrackvar is used to change the current background music that is playing. This command works like the starttrack command but the former can accept gamevars whereas the later accepts only constants.
<track#> is literally the track number of the current episode (which can be detected with the gamevar VOLUME) as defined by the music command.
Example: this will start the music track from episode 3, level 2.
gamevar episode 2 0 gamevar level 1 0 getuserdef[THISACTOR].volume_number TEMP setuserdef[THISACTOR].volume_number episode starttrackvar level setuserdef[THISACTOR].volume_number TEMP