doesn't play sound in vuforia

Hi. I learn vuforia. In field I have gameObject. Instead of main camera, I have AR Camera, which has Audio Listener. To my game Object I adв Audio Source. And attach script to this gameObject. In script I have public field: public AudioClip shootSound; In unity I put to this variable mp3 file. And when I try in constructor start this code:

     void Start ()
     {
             source = GetComponent<AudioSource>();
         source.PlayOneShot(shootSound);
     }

I heard very short sound and thats all. How can I write code, to play audio to end?