How to get duration value from windows media services 9

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I'm using windows media services 9 to provide streaming service and would like to make sure users can only play within specified interval to prevent abuse. The media server reads and from asx file and the player can start and end at the correct offset. I can get the start offset at AuthorizePlayEvent using

IWMSContext.GetQwordValue(WMSDefines.WMS_PRESENT_START_TIME,WMSDefines.WMS_PRESENT_START_TIME_ID, out dec, 0);

But I'm having problem getting the duration or end offset. I know windows media server writes log that contains c-starttime and x-duration. But the x-duration here doesn't seem to be what I want. I like to detect the <duration> that gets passed from asx file at either AuthorizeOpenEvent or AuthorizePlayEvent. If the starttime and duration are not valid, I would like to fail the authentication and stop playing. Is this possible?

Thanks!

[JAMES_911]

I am not sure if WMS_PRESENT_DURATION_LO is meant to be a "updateable" value or not. If setting that context value does not work, one other idea is that there is a WMS_USER_ID in User context which I believe is unique for each client that is connected.

As long as you can map this to some data structure that maintains when the client was connected, you can check periodically (say during heartbeat) and see if any client has gotten past the time it is supposed to play and if it has, simply disconnect it. There might be other/better ways to do this, but this was the first thing that came to my mind. HOpe this helps.