Blood potions allow for feeding via potions, anywhere and anytime. And I apologize for my incomplete info, I've just never played as a vampire...I prefer hunting them.
So do I, but I got hyped up into playing a vampire and setting her up for Dawnguard...and....ya....
May have to add myself to my fictional suicide list...

4. You can only feed on non sleeping NPCs if:
a. You're performing a quest that requires you to turn them. This is done via vampiric seduction, and them interaction.
b. if they're thralls at castle Volkihar.
5. Blood potions confer the same benefits as feeding. You get them via Volkihar side quests. They also regenerate 100 points of health.
So basically the whole part in the trailer where the Vampire character bites the NPC on the neck while standing up was BS?
I CURSE YOU TODD HOWARD!!! AWAY!!! (Said in the female dunmer voice in Morrowind, it's what she said to vampires).