如何用js给<object>(视频对象)的url赋值？高手快来接分。

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<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
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</HEAD><BODY>
<OBJECT id=WindowsMediaPlayer1 name="player" height=360 width=480 classid=clsid:6BF52A52-394A-11D3-B153-00C04F79FAA6>
<PARAM NAME="URL" VALUE="aaaaaaa">
<PARAM NAME="rate" VALUE="1">
<PARAM NAME="balance" VALUE="0">
<PARAM NAME="currentPosition" VALUE="0">
<PARAM NAME="defaultFrame" VALUE="">
<PARAM NAME="playCount" VALUE="1">
<PARAM NAME="autoStart" VALUE="-1">
<PARAM NAME="currentMarker" VALUE="0">
<PARAM NAME="invokeURLs" VALUE="-1">
<PARAM NAME="baseURL" VALUE="">
<PARAM NAME="volume" VALUE="50">
<PARAM NAME="mute" VALUE="0">
<PARAM NAME="uiMode" VALUE="full">
<PARAM NAME="stretchToFit" VALUE="0">
<PARAM NAME="windowlessVideo" VALUE="0">
<PARAM NAME="enabled" VALUE="-1">
<PARAM NAME="enableContextMenu" VALUE="-1">
<PARAM NAME="fullScreen" VALUE="0">
<PARAM NAME="SAMIStyle" VALUE="">
<PARAM NAME="SAMILang" VALUE="">
<PARAM NAME="SAMIFilename" VALUE="">
<PARAM NAME="captioningID" VALUE="">
<PARAM NAME="enableErrorDialogs" VALUE="0">
<PARAM NAME="_cx" VALUE="12700">
<PARAM NAME="_cy" VALUE="9525">
</OBJECT>
<SCRIPT LANGUAGE="JavaScript">
<!--
alert(WindowsMediaPlayer1.url)
WindowsMediaPlayer1.url = 'aaaaaaaaaaaaaa.mp3';
alert(WindowsMediaPlayer1.url)
//-->
</SCRIPT>
</BODY>
</HTML>