var track1 : AudioClip;
var track2 : AudioClip;
   
audio.clip = track1;
audio.Play();
   
var audio1Volume : float = 1.0;
var audio2Volume : float = 0.0;
var track2Playing : boolean = false;
   
function Update() {
     fadeOut();
   
     if (audio1Volume <= 0.1) {
         if(track2Playing == false)
         {
           track2Playing = true;
           audio.clip = track2;
           audio.Play();
         }
   
         fadeIn();
     }
}
   
function OnGUI()
{
     GUI.Label(new Rect(10, 10, 200, 100), "Audio 1 : " + audio1Volume.ToString());
     GUI.Label(new Rect(10, 30, 200, 100), "Audio 2 : " + audio2Volume.ToString());
}
   
function fadeIn() {
     if (audio2Volume < 1) {
         audio2Volume += 0.1 * Time.deltaTime;
         audio.volume = audio2Volume;
     }
}
   
function fadeOut() {
     if(audio1Volume > 0.1)
     {
         audio1Volume -= 0.1 * Time.deltaTime;
         audio.volume = audio1Volume;
     }
}