[AS3]flv视频播放器NetStream.play播放时遇到的问题(源代码示例)

代码中 play flv 格式的文件.没问题.
为何 play mp3 格式的时候. 就找不到了呢? 根目录存在 b.mp3 文件
错误提示是 Stream not found: b

package  
{ 
    import flash.display.Sprite; 
    import flash.display.Stage; 
    import flash.media.Sound; 
    import flash.media.Microphone; 
    import flash.media.SoundChannel; 
    import flash.media.SoundTransform; 
    import flash.media.SoundLoaderContext; 
    import flash.net.*; 
    import flash.events.*; 
    public class rtmpPlayer extends Sprite  
    { 
        private var _sound:Sound; 
        private var _netNc:NetConnection = new NetConnection(); 
        private var _ns:NetStream; 
        private var nsClient:CustomClient = new CustomClient(); 
        private var soundXForm:SoundTransform = new SoundTransform(); 
         
         
        public function rtmpPlayer() { 
            soundXForm.volume = 0.5; 
             
            _netNc.addEventListener(NetStatusEvent.NET_STATUS,onNetStatus); 
            _netNc.addEventListener(SecurityErrorEvent.SECURITY_ERROR, securityErrorHandler); 
            _netNc.connect(null); 
            //CuPLayer.com:addEventListener(Event.ENTER_FRAME, onEnterFrameHandler);  
        } 
         
        private function onNetStatus(event:NetStatusEvent=null):void { 
            //CuPLayer.com:handles NetConnection and NetStream status events 
            switch (event.info.code) { 
                case "NetConnection.Connect.Success": 
                    //play stream if connection successful 
                    connectStream(); 
                    trace("NetConnection.Connect.Success"); 
                    break; 
                case "NetStream.Play.StreamNotFound": 
                    //error if stream file not found in 
                    //CuPLayer.com:location specified 
                    trace("Stream not found: " + _soundUrl); 
                    break; 
                case "NetStream.Play.Stop": 
                    //do if video is stopped 
                    //CuPLayer.com:videoPlayComplete(); 
                    trace("do if video is stopped"); 
                    break; 
            } 
            //trace(event.info.code); 
        } 
         
        private function connectStream():void { 
            _ns = new NetStream(_netNc); 
            _ns.addEventListener(AsyncErrorEvent.ASYNC_ERROR,doAsyncError); 
            _ns.addEventListener(NetStatusEvent.NET_STATUS, onNetStatus); 
             
            _ns.client = nsClient; 
             
            //_ns.play("b.flv"); 
            _ns.play("mp3:b"); 
             
            //_ns.soundTransform = soundXForm; 
        } 
         
        private function securityErrorHandler(event:SecurityErrorEvent):void { 
            trace("securityErrorHandler: " + event); 
        } 
         
        private function asyncErrorHandler(event:AsyncErrorEvent):void { 
             
        } 
         
        private function onEnterFrameHandler(event:Event):void { 
            //if(_ns) trace(_ns.bytesLoaded + "==" + _ns.bytesTotal); 
        } 
         
        public function doAsyncError (event:AsyncErrorEvent):void { 
            trace("asyncErrorHandler: " + event.text); 
        } 
    } 
} 
 
class CustomClient { 
    public function onPlayStatus( info:Object ):void{ 
        switch ( info.code ){ 
            case "NetStream.Play.Switch": 
                break; 
            case "NetStream.Play.Complete": 
                trace("soundCompleteHandler"); 
                break; 
            default: 
                for ( var a:String in info ) {  
                trace(a + " " + info[a]); 
                } 
                break; 
        } 
    } 
     
    public function onCuePoint(info:Object):void { 
        trace("cuepoint: time=" + info.time + " name=" + info.name + " type=" + info.type); 
    } 
     
    public function onMetaData(info:Object):void { 
        trace("metadata: duration=" + info.duration + " width=" + info.width + 
" height=" + info.height + " framerate=" + info.framerate); 
    } 
}