netstream.publish()方法保存为mp3格式为什么不行解决思路

         ns=new NetStream(nc);
         mic.addEventListener(StatusEvent.STATUS,this.onMicStatus);
                       
         ns.addEventListener(NetStatusEvent.NET_STATUS,onStatusHandler);
         ns.attachAudio(mic);
         
          if(this.micString=="Microphone.Unmuted")
            {     
                 labeltext.text="录音中..."+i;
                 this.time.start();
                   [color=#FF0000] ns.publish("myMP3Stream","record");[/color]
            }