Blocking facebook Videos & Chat

Hi, 

We have Fortigate 60E in our network. I tried to block facebook chat and videos while allowing facebook which didn't work. All the users are accessing facebook through web i-e //https. I have done settings in 'Application Control' where i have added Application Signature for facebook Chat & Videos = Block. But it's not working. What other configuration or settings are required to Block only Facebook Chat and Videos? Need your kind response. Thank You