With the blitz of superheroes invading the big-screen and television, the pressure of creating an iconic theme song can be just as stressful -- and just as important -- as an updated costume or origin story.

Five composers who have scored recent and upcoming superhero appearances -- including CBS' "Supergirl" Marvel's "Avengers" franchise, the "Fantastic Four" reboot and the recent "Ant-Man" -- talked about their craft at a Comic-Con International panel. Moderator Anthony D'Alessandro played a clip from each of the five composers' recent superhero work as he introduced each.

First up was composer Blake Neely, introduced along with a piece from the '"Supergirl" pilot. Neely -- who's also working on The CW's "Arrow" and "The Flash" -- admitted he wanted to take on "Supergirl," after being asked by executive producer Greg Berlanti, "because I'm completely greedy and I want to work on every DC character.

What spoke to me, was that it's completely different from 'Arrow' and 'The Flash' in that, you know, it's a cousin of Superman, so it's my chance to do something traditional and an homage to the guy that inspired most of us here on stage: John Williams," said Neeley.

Neely also talked about juggling the three shows -- and a fourth coming in The CW's "Legends of Tomorrow" -- and the constant grind in writing music for TV. He explained that he gets about ten days to write per show, but it helps since he has a team and can write fast. He also admitted to reusing cues -- something "Twitter seems to remind me of a lot," he said, getting a laugh from the audience.

Brian Tyler, who had previously scored "Iron Man 3" and "Thor: The Dark World," talked about writing the "Avengers: Age of Ultron" score, showing a clip of a dramatic moment in the film's final battle. Tyler talked about the jugging involved in incorporating previous themes from the Marvel Universe for "Age of Ultron," as well as creating themes for the film's new characters and a specific theme to accompany Hulk and Black Widow's subplot.

"You really are dealing with a lot of themes, but I think it really works in a way that I always felt 'Star Wars' did. You had a Leia theme. You had a Force theme. You had Luke... you had all these different themes. In a way, we treated it like that," explained Tyler. "Where you try to connect them and do something new with the ones from before. And then you create something completely out of the box," citing the Vision theme as a prime example.

There was no clip shown for this summer's "Fantastic Four," but a long clip of Marco Beltrami's score was played -- something he referred to as a prelude in the film that he worked on along with Philip Glass. The composer explained that for the film, "the important thing was that to capture the innocence and curiosity, the scientific minds of these kids that come together." He also admitted he hadn't seen the previous two FF films.

The explosive sandstorm scene from "Mad Max: Fury Road" was shown to the crowd, and composer Junkie XL -- real name: Tom Holkenborg -- explained how he was recruited to work on the film, receiving a phone call from a Warner Bros. executive and three hours later, being on a plane to Sydney, where he watched a rough cut of the film.

"The first shot was the guitar player just screaming," said Junkie XL. "It was clear, the whole movie was so visceral and so aggressive, and so over-the-top -- the first thing that came up to me was, 'Okay, let's make a rock opera.'" He later told a story about how his musicians literally distorted microphones during their recording session by playing so loud.

INTERVIEW: Christophe Beck Composes "Ant-Man's" Big Score

A scene from "Ant-Man" was shown next, with the insect-sized hero riding through drainpipes amidst an army of ants, accompanied by a soaring score. Composer Christophe Beck spoke about working on the Marvel Studios project, saying: "It's pure chaos and confusion from beginning to end," and that he was lucky to work with director Peyton Reed, as the two did their first films together. Beck said the biggest problem was getting "the people that mattered to just sit down and listen to what I was doing. They were just so busy, and scrambling, trying to finish the movie that the few times I did get their attention, I had to make the most of it. Beck called working on the film a "very difficult process, but totally rewarding."

The panel turned to audience questions, with someone asking the panel their favorite specific scale or cadence to use on superhero themes.

"You want to hear something nerdy?" asked Neely. "So when I first started 'Arrow,' I decided I would only write within A, A flat or A sharp," he said to laughs. "Then when I started 'Flash,' guess what keys I picked... It only lasted about two episodes, but there you go."

Tyler took on a question about using previous superhero themes as inspiration or forgetting them when taking on a new superhero project.

"That depends. I remember coming on board for 'Iron Man 3' and 'Thor: The Dark World,' which were going to Phase 2 of the Marvel Universe, and they wanted a kind of reset -- so in that sense, you get told they want something new. Tyler explained that for "Age of Ultron" the studio wanted to tie it to the first Avengers movie. "I always love using source material just because I'm a huge movie fan," adding he appreciates the continuity and nostalgia it can build.

Tyler cited Michael Giacchino's recent use of John Williams' score in "Jurassic World" as good example of using previous scores within a new one. "I think there's a balance but it depends on the project. I do it when I can," said Tyler.

When asked what piece of music inspired them to first become composers, virtually the entire panel agreed it was John Williams' work on "Star Wars." Beltrami said Ennio Morricone's "Once Upon A Time In The West," but Junkie XL went another way, citing Pink Floyd's "Dark Side of the Moon, and told a story of taking the record to school when he was seven, "and the kids started crying, and the teachers called my parents."

When asked about creating "big" superhero themes in today's studio system, Tyler said, "I find that there's a bit of a resurgence, now that there are lot of producers that grew up with 'Star Wars' and 'Superman' and all that -- I think we're on the upswing with that, hopefully."

:The scariest thing a producer can tell you is -- he can tell you, 'Write me something beautiful, big, grand, heartbreaking,'" said Neely. "But as soon as they say 'iconic,' I want to vomit. Because who knows what iconic is? It's only iconic years from now. It's a big test, right?"