This is one of those little nuggets of knowledge you weren’t even aware had an answer until you heard the question. Who is Frank Underwood talking to when he speaks directly into the camera? With shows like The Office you know the characters are speaking to a film crew and that fact is established early on in the series – but Frank? NOPE, he just goes about his merry day not telling anyone anything and spoutin’ line after line of Underwoodisms to whoever (or whatever) will listen.
As for who Spacey says he’s talking to, well, he jokingly (albeit realistically) says it’s “people on a 10-hour Netflix binge, sucking on boxed wine.” No dice, Space – I’ll keep my Angry Orchards and jalapeno potato chips in lieu of wine kthx.