As Peter says, getting a definitive list of those IPs is going to be tough, particularly for Youtube as that will use servers in Google’s systems as well as ones specifically registered to Youtube IP addresses.
For Twitter, the Players won’t be connecting to Twitter at all (assuming you’re using the official Twitter integration). All that goes via the CMS so it might be easier to allow the CMS to connect out to anything, rather than try and detect traffic going to Twitter specifically.