Not sure if this will help but I will try. My suggestion is to use advanced track options like "Detailed Log" and "Extended Log" if you have enabled one or more of these blades on the Layer: Applications & URL Filtering, Content Awareness, or Mobile Access
So if you create a new policy rule for Youtube in the "Service and Application" column and set the "Track" column to "Extended Log" the URLs will show in the Logs view hereafter. Don't know if you have already done this.
- Detailed Log - Equivalent to the Log option, but also shows the application that matched the connections, even if the rule does not specify an application. Best Practice - Use for a cleanup rule (Any/Internet/Accept) of an Applications and URL Filtering Policy Layer that was upgraded from an R77 Application Control Rule Base.
- Extended Log - Equivalent to the Detailed option, but also shows a full list of URLs and files in the connection or the session. The URLs and files show in the lower pane of the Logs view.
Addditional logging adds a performance impact.
This might also be relevant which is is added automatic I believe when you use an application in the "Service and Application" column.
- Accounting - Select this to update the log at 10 minute intervals, to show how much data has passed in the connection: Upload bytes, Download bytes, and browse time.