Soundtrack sounds too fast

1

I am playing a soundtrack in my Flash movie :

function callback1() {
my_sound.start(0,1000);
}

my_sound = new Sound();
my_sound.loadSound(“mySound1.mp3”, true);
my_sound.onSoundComplete = callback1;
my_sound.start(0,1000);
gotoAndStop(“4”);

the track itself is fine when played in iTunes, but it plays too fast when it runs in my app. What could be the cause?