Audio falloff from movie stream

I neeed help with a Movie-Stream (ogg-file) in a web-player. It works fine, but the Audio have no falloff. I found old simillar questions here, but no solution.

I have only one Audio-listener (Camera) in my Scene.

Here is the script: #pragma strict

 @script RequireComponent(typeof(AudioSource))
 
 public var moviePfad : String;
 public var audioMaxDistance : float = 50;
 public var loop : boolean = true;
 
 private var movieTexture : MovieTexture;
 protected var streamReady : boolean = false;
 
 function Start ()
 {        
     StartCoroutine(StartStream(moviePfad));
 }
 
 function StartStream (url:String)
 {
     var videoStreamer : WWW = new WWW (url);
     movieTexture = videoStreamer.movie;
     audio.clip = movieTexture.audioClip;
 
     while (!movieTexture.isReadyToPlay) {
         yield;
     }  
     audio.rolloffMode = AudioRolloffMode.Linear;
     audio.minDistance=1; 
     audio.maxDistance=audioMaxDistance;  
     //audio.dopplerLevel = 0;
     //audio.panLevel = 1;
     audio.loop = loop;
     audio.Play ();
     movieTexture.loop = loop;   
     movieTexture.Play ();
     streamReady = true;
 }
 
 function Update () {
 
     if (streamReady) {
         renderer.material.mainTexture = movieTexture;
     }
 }