var nc:NetConnection = new NetConnection();
nc.connect(null);
var ns:NetStream = new NetStream(nc);
myVideo.attachVideo(ns);
ns.play("myVideo.flv");
//創建一實例MC獲取myVideo.flv的聲音
_root.creatEmptyMovieClip("Soundmc", _root.getNextHighestDepth());
Soundmc.attachAudio(ns);
var VideoS:Sound = new Sound(Soundmc);
//設置聲音大小
VideoS.setVolume(50);

在網路上找到的好東西！檔案來源：夏日之夜(Guoyl)