A) living under a rock.
B) NOT living on social media sites
The trailer was leaked, initially, and then officially released by Marvel so we can have it in all of it's explosive HD goodness. And yes, I'm going to share it here because it's awesome. And it's my blog, so I can do what I want.
Warning: This trailer looks all 'doom and gloom' with melodramatic over AND undertones, but let's be honest. It's Marvel and Joss Whedon. There will be plenty of snappy one-liners and slapstick comedy to numb us all to the apocalyptic, world decimating, Michael Bay-ish destruction porn.