#in your script you may have something like this

if ( $ARGV[0]  == 1 ) {
     # your mp3 playing code
}else{
     # we run the mp3 code & continue doing what we want/need
     # like this
     my $pid = system(1,"$0 1");
     # you could monitor the pid yourself and/or kill the process when exiting .. it's up to you.

}