Marvel Studios: Assembling a Universe is a one-hour special documentary that aired on ABC on March 18, 2014. The documentary showed exclusive looks at all the previous films and one-shots as well as sneak peeks of Captain America: The Winter Soldier, Guardians of the Galaxy, Avengers: Age of Ultron and future episodes of Agents of S.H.I.E.L.D..
(From the official press release)
Marvel's first television special documents the exciting story behind Marvel Studios and the Marvel Cinematic Universe, featuring exclusive interviews and behind-the-scenes footage from all of the Marvel films, the Marvel One-Shots and Marvel's Agents of S.H.I.E.L.D. Viewers will walk a clear path through this amazing and nuanced universe, featuring sneak peeks at the future of ‘Marvel's Agents of S.H.I.E.L.D.' on ABC, new footage from Marvel Studios' upcoming theatrical releases, Captain America: The Winter Soldier and Guardians of the Galaxy, and a sneak peek at the upcoming Avengers: Age of Ultron and Ant-Man.