It's going to be a problem for you because most of the video on facebook is actually hosted by someone else and is not actually streaming(udp). For example youtube. Basically most of the video on facebook is just a link to a video host. Therefore you have to block all links in order to make this work. Your best bet is to go with an option like dyndns and set it up to block as many known video hosts as you can find. To be honest however I would block facebook outright.
Someone else may know a trick that I don't but it looks like you have a problem on your hands.