WFilter 4.1 has a url library so you can block “Streaming Media” category to block video websites.Proceed as follows:

Step 1. New a “blocking level” in “Policy Settings->Blocking Levels”, then check “Block webpages by categories” and select new in “Category”:

Step 2. Deny “Streaming Media” category and save setting:

Step 3. Apply this blocking level to computer in “Policy Settings->User-device List”:

Step 4. Visit a video website and check result:

Step 5. You can see the blocking records in “Current Online->Real-time Blocking”: