I'm not saying it's convenient, but it's a neat trick I didn't realize until today: If you have an AppleTV and a Mac, you can hit New Movie Recording (cmd-opt-N) in QuickTime, switch the input to your AppleTV (click the little chevron next to the red Record button to change this), do the same for the microphone... and you can record the A/V of whatever's on the TV.

I sort-of assume there's a flag somewhere that keeps you from recording HBO & movie rentals? It's sorta analog-hole-exploiting (but digital??), otherwise? I just tested it with a YouTube channel.