Re: Preventing videos/ads from playing
If you're looking to blacklist sites, there are a number of different ways to do this. Your best bet is probably to look into add-ons/extensions for the browser or browsers you use for site blacklisting.
If what you're trying to block is actually an ad then I'd use an ad blocker extension such as Adblock Plus in your browser or browsers.
If you want something that blocks a given website for all browsers you use you can add an entry to your hosts file using 127.0.0.1 as the IP address and then it cannot be opened. See here or here for additional information.
Presenting the willfully ignorant with facts is the very definition of casting pearls before swine.