The creator says this:
"I recreated the Avengers Trailer from February 2012 with animation clips from 1960's Marvel TV cartoons. The only cheat was Nick Fury, but the clips are from his first appearance in an "Iron Man" episode from 1995. I also borrowed a Paramount logo from the same era to fit with the look. Black Widow was a tough find since she was a shadow character and appeared very rarely."