SPOILER WARNING: This interview contains spoilers for Marvel Studios' "Agent Carter" short film.

Not content with simply producing undeniably successful feature films -- 2012's "Avengers" and this year's "Iron Man 3" both grossed more than a billion dollars worldwide -- Marvel Studios branched into short films with its "Marvel One-Shots" series.

The shorts appear as extras on Marvel Studios home releases, with the first two starring Clark Gregg as Agent Phil Coulson, and only running for about four minutes each. With "Item 47," released with "The Avengers'" Blu-ray, the running time grew (12 minutes) along with the budget, and Marvel Studios co-president Louis D'Esposito stepped in to direct. That upward mobility continues with "Agent Carter," also directed by D'Esposito and starring Hayley Atwell -- reprising her "Captain America: The First Avenger" role of Agent Peggy Carter -- and Bradley Whitford as her sexist boss, Agent Flynn.

Set shortly after the events of "Captain America: The First Avenger," "Agent Carter" is 15 minutes long, and appears as an extra on the "Iron Man 3" Blu-ray and HD digital releases. CBR News spoke with D'Esposito and Marvel One-Shot executive producer Brad Winderbaum at Disney's Burbank headquarters, discussing why the "One-Shots" program is important to Marvel Studios, the challenge of executing big ideas in short films and the significance of "Agent Carter's" "Zodiac key."

CBR News: Louis, Marvel Studios has done four "One-Shot" short films now, and while "Agent Carter" seems to be a little bit of a bigger production than its predecessors, it's definitely the longest one. These shorts are not something that Marvel has to do -- certainly, you have a very successful feature program -- what inspired doing the shorts, and sticking with it?

Hayley Atwell uncovers the machinations of the Zodiac key in Marvel's "Agent Carter" one-shot

Louis D'Esposito: They're fun, first of all. And I think it gives us a chance to tell stories that we normally wouldn't tell, and then bring that cinematic experience to the home viewer. Brad produced the first two -- he had them done outside of Marvel, because we didn't think we had the time. They came out great, we looked at them and we said, "Why don't we take this on ourselves? We already have so much on our plate, what the hell, let's add a little bit more work." [Laughs]

We developed "Item 47" at that time, and we made a conscious effort to make it bigger. We doubled the budget, I believe; we doubled the length of it. We only had really one location for the other ones; we shot in two or three days. ["Item 47"] was a four-day shoot in and of itself, we had multiple locations and sets. And then we did the same thing on "Agent Carter." We doubled that budget. We didn't double the shooting time, but the scope of it is much bigger. It's set in a period, there are more actors involved, the scale's bigger, there are three fight scenes -- we've never had that in any of [the previous One-Shots].

I think there comes a point where you can only get so big, though. It's not just the scope of it; it's telling the best story, and finding that story we want to tell -- whether it's connectivity to the Marvel Universe, or it's highlighting a character. In the case of Hayley, it's a little bit of both. We wanted to tell Peggy Carter's story -- she's been left back in the '40s. Announcing to the world that she was running S.H.I.E.L.D. with Howard Stark is a great connectivity.

Also, we have the fun of it. Seeing such a wonderful actress in a man's world have her comeuppance on Bradley Whitford. Hopefully it's a rewarding and fulfilling experience for all Marvel fans.

Is it fair to say then, after four in a row, that the plan going forward, at least for now, is to keep doing these?

D'Esposito: I think we have a couple more planned.

Brad Winderbaum: It's hard to look too far out in the future, but it's certainly something we want to keep doing, as long as fans keep watching them and liking them.

D'Esposito: It's also a balancing act of our time. They require a lot of work. We shot ["Agent Carter"] when we were in post for "Iron Man 3." The second editor on "Iron Man 3," Peter Elliot, became our editor. ["Iron Man 3" director and co-screenwriter] Shane Black, who was in one editing bay, came over and watched the first rough cut. It was just assembled, and that's when we started talking. "Do you want to be the disembodied voice?" He said, "Yeah, I'll do it, sure!" He did it, and he added his touches with the "niners" and the "fivers" and whatever he was saying.

Director Louis D'Esposito (L) on the set of "Agent Carter" with Bradley Whitmore

It's that kind of process. We were all together in the post-production on a film. "Iron Man 3" was a difficult post because of the time that we had. We consciously made an effort to shorten it because of scheduling issues. So we put that extra pressure on us, and then we said, "Uh oh, we committed to this short, we have to do that, too." It was a lot of work.

There's probably no shortage of ideas for potential shorts, between the amount of characters and elements in the Marvel world, and the things that may not get quite as explored as you'd like them to be in the features. Is that the case?

D'Esposito: Absolutely. We have a small brain trust, and they sometimes throw out the wackiest ideas. Obviously, reality hits you in the face and there are only certain things you can do. It always seems to lead us to the story that we should have been telling in the first place. A lot of times we're, "A young Nick Fury! A new Black Panther! A young Black Widow back in Russia!" We're going through all these ideas.

Winderbaum: A lot of them have finished scripts.

D'Esposito: "What about something on Asgard?" "We can't be in Asgard, that's all CGI." "Can we have the Hulk for half of a second?"

It's all those ideas, and it's a big funnel, and we throw them in, and then the one we should be telling starts to [surface]. We've always had this Peggy Carter [idea] sitting around. [Hayley Atwell]'s availability happened to coincide with our shooting schedule. She loves the character, and wanted to do it, and that's how it came to be.

It seems to be a testament to the strength of Marvel Studios at this point to have Hayley Atwell come back for a short, and have an actor like Bradley Whitford appearing in a supporting role of a short.

D'Esposito: Isn't that fantastic? It is a testament to who we are now, and our brand. We cast shorts like we cast our films. We call our casting director Sarah Finn, she reads it, we explain to her what we want in the characters and she sends over a list. I'm looking -- "That's Bradley Whitford. Yeah, we want Bradley Whitford!"

It surprises us, too, but I think the quality now of the shorts speak for themselves. Usually you hear "short film," and you think, "I'm doing someone a favor." "Is it a student film?" Which are all great and wonderful, but when you're asking such big name talent to put their face on something, there has to be trust.

The "Agent Carter" short involves the title character looking for the "Zodiac key." Zodiac has meant several different things over the years in Marvel Comics. Was there a specific motivation for its inclusion, or is it more a nod to the greater Marvel world?

D'Esposito: We had our protagonist and antagonist; we needed a MacGuffin. When looking through the Marvel bag of MacGuffins -- Zodiac, it sounds cool, it had a great emblem. It really wasn't imperative we knew what it was at this time, but we knew it would present opportunities in the future.

The "Agent Carter" Marvel Studios one-shot is available on the "Iron Man 3" Blu-ray, out Sept. 24, and the HD digital download, available now.