在动作脚本3中嵌入mp3不起作用

我对actionscript 3有一个问题,特别是在使用embed标签时.我有这个代码:

[Embed(source = "sound.mp3")]
private static var soundClip:Class;


var sound:Sound = (new soundClip()) as Sound;
trace(sound.length);

var sound:Sound = (new soundClip()) as Sound;
trace(sound.length);

[Embed(source = "sound.mp3")]
private static var soundClip:Class;


var sound:Sound = (new soundClip()) as Sound;
trace(sound.length);

当我测试电影时,我得到以下输出:4501,923这是sound.mp3长度,以毫秒为单位.但是,原始声音是13.000毫秒.

怎么可能,有人可以帮我吗？

谢谢.