IS there a command to start/stop audio that plays across frames??

[AS3.0]

Yes for as3/air:

stop all sounds:

SoundMixer.stopAll(); 

to play a sound, give your mp3 in the library a linkage name such as login_song and the next part where it says 1 that's the amount of times to loop it in this call: playSound(login_song,1);

playSound(login_song,1);
function playSound(a,amount){
var audio:Sound = new a();
audio.play(0,amount);
}