Can't pass name of file to Windows Media Player in asp.net dynamically. Is this even possible?

I have a asp.net page done in C#.  In the page, I have added a windows media player object.  From the code behind, I can set various labels on the page that provide the title of the video to watch.  But, whenever I try to pass the name of the actual file to play, it's empty and no file plays.  (I did try hard coding a value for the file, and it will play).  Any idea what I'm doing wrong with trying to pass  the name of the file to be played in WMP?  Is it even possible to dynamically pass file names to windows media player? 
My aspx page <object id="MediaPlayer" classid="clsid:22d6f312-b0f6-11d0-94ab-0080c74c7e95" codebase="http://activex.microsoft.com/activex/controls/mplayer/en/nsmp2inf.cab#version=5,1,52,701" standby="loading microsoft windows media player components..." type="application/x-oleobject" width="640" height="480"> <param name="filename" runat="server" id="filename" /> <pa ...