Help with flash Vars - javascript/php

I'm using a script on an html page, to record a flash video. Part of the code is this:

<script type="text/javascript">
               // <![CDATA[
               var so = new SWFObject("recorder.swf", "recorder", "620", "470", "9", "#000000");
       	       so.addParam('flashvars','filename=sample&rtmpPath=rtmp://6tv610x0z6k.rtmphost.com/sa/&finishURL=play.html')
               so.write("recorder");
               // ]]>
               </script>

Code (markup):

I'd like to add the ability to have each recording get a different file name. I was told "every record will have different name if you will put unique "filename" variable for each record. (using php for example)"

Can you give me some guidance/example as how to 'put unique "filename" variable"?
thanks