Start video on a determinated second

Hello,
I would like to start a video on a determinated second.

I try to use->>> so.addVariable('start','5');

But it does not work.

What can I do??

Thank you

<script type='text/javascript'>
var so = new SWFObject('player.swf','mpl','470','320','9');
so.addParam('allowfullscreen','true');
so.addParam('allowscriptaccess','always');
so.addParam('wmode','opaque');
so.addVariable('file','http://content.longtailvideo.com/videos/flvplayer.flv');
so.addVariable('start','5');
so.write('mediaspace');
</script>