I actually opened mine - it's a 5 minute mini that talks mostly about the opening/ending action sequences and how they evolved each characters fighting style. Actual summary on the website is:
"
Marvel’s Avengers: Age of Ultron opens huge and only gets bigger for the final battle! To create such explosive action sequences featuring all of our favorite heroes, the filmmakers challenge themselves in new ways, always pushing their craft a step further. Discover the unprecedented amount of work that goes into bringing these scenes to the big screen, from the page written by Joss Whedon to the final sequence as seen in theaters. Learn how the team lays out these breathtaking moments using never-before-seen animatics and pre-visualization. Join the actors and stunt team on set, and visit the wizards in postproduction for the final touches. Be part of the film’s evolution from start to finish in this exclusive behind-the-scenes mini documentary."
The annoying thing is that the video is only on Marvel's offers page for Ultron
and it'll actually expire end of May 2016
You can at least save the mp4 to desktop, but...