Getting NetStream.Play.FileStructureInvalid when trying to stream local MP3

programming flash
1 

var connection:NetConnection;
var stream:NetStream;
var streamURL:String;
            
function loadStream(url:String):void {
    streamURL = url;
    connection = new NetConnection();
    connection.addEventListener(NetStatusEvent.NET_STATUS, netStatusHandler);
    connection.connect(null);
}
function netStatusHandler(event:NetStatusEvent):void {
    trace(event.info.code);
    switch (event.info.code) {
        case "NetConnection.Connect.Success":
            connectStream();
            break;
        case "NetStream.Play.StreamNotFound":
            trace("Stream not found: " + streamURL);
            break;
    }
}
function connectStream():void {
    trace("try to play");
    stream = new NetStream(connection);
    stream.client = this;
    stream.addEventListener(NetStatusEvent.NET_STATUS, netStatusHandler);
    stream.play(streamURL);
}

loadStream("testsong.mp3")

Anyone know anything about this?