When it came to adapting the popular “Ratchet & Clank” video game series, the filmmakers were certain of at least one thing: Voice actors James Arnold Taylor and David Kaye had to reprise their franchise roles as Lombax mechanic Ratchet and little sentient robot Clank.

"It's like making a 'South Park' movie without Matt [Stone] and Trey [Parker]," producer Brad Foxhoven told a gathering of journalists at WonderCon, where he was joined by director/co-writer Kevin Munroe, and stars Taylor, Kaye and Bella Thorne. "You can't really do that. There were moments where people that were outside the circle of the film were like, 'Hey, wouldn't it be great if we replaced this person?'"

"That would make a great poster for some other movie," Munroe replied.

"I was worried that it didn't really matter," Kaye added. "But when this thing broke that it was going to be a film, trending on Twitter was the fact that [Taylor] and I were still in it."

Opening Friday nationwide, the 3D animated sci-fi comedy adventure retells the events of “Ratchet & Clank’s” 2002 game debut, in which the two beloved characters meet while attempting to save the galaxy from destruction at the hands of Chairmen Drek and the Blarg. However, it also weaves in elements from later entries in the series, such as Doctor Nefarious and the Galactic Rangers, and even introduces a new character.

Video-game adaptations have a rough history in Hollywood, but Foxhoven and Munroe were determined to honor the source material. "There's a high expectation going in," Foxhoven said. "You've spent so much time, you're so intimately involved. It's hard to make one of these things work. Gamers are naturally vocal. They have no problem saying what they feel or what they like."

The producer hopes longtime fans will appreciate how closely the filmmakers worked with the developers at Insomniac Games. "We [believed] that, from the very beginning, it was the ticket to do this film," he said. "That's what helped us be true to the core. It's like J.K. Rowling: If you don't have her involved in ‘Harry Potter,’ you're not making ‘Harry Potter.’ And that's the same thought we had."

For the first time, Kaye and Taylor – as well as Jim Ward, who voices Captain Qwark in both the games and the movie -- were able to record their performances together, giving them the chance to play off each other in the way they've always done so well onscreen. "That was the coolest part, was that we were all together," Taylor said. "I was in a separate little booth, because they needed to be able to isolate David's and my voices, because we talk together so much. But we were all in the same room together."

"I was the only one not invited to their little three-way thing, when they all got to be in the studio together," lamented Thorne, who plays new character Cora. "When I got the offer for the film, I did a lot more research and watched a bunch of videos, and I kept looking for my character. And then they told me that I'm literally stepping in with these big people that have been voicing these characters -- I'm literally stepping in with the big dogs, so that was really cool."

In addition to the movie, Ratchet and Clank star in a new game that retells their origin, in a loose remake of their 2002 debut. Thanks to the relationship between Insomniac and the filmmakers, the two will be closely connected. "They're very intertwined, I think," Munroe said. "I kind of don't know where the line is. And then you see it in the game. It's the game based on the movie based on the game."

The film and the new game provide Taylor with the opportunity to voice Ratchet's backstory, which he missed out on the first time around (he didn’t join the franchise until 2003’s “Going Commando”). "That was one of the coolest things for me," he said. "It was really cool that they're going to go back and retell it."

"We get to go deeper into that story of how they met," Kaye added. "There's a lot of tender moments in the film. If robots could cry, there was a moment there."

That emotional connection is what Munroe sees as the heart of the film. "Once you have that core, and that through-line, and you have these two guys, and it's an origin story of what both of them bring to the table and how they learn to be together -- if you've got that as your spine, you can do it with sock puppets at that point," he said. "If that works, it works. And then everything else is there to enhance the strong spine that's there."

Although the filmmakers took care to appeal to the fans that have played "Ratchet & Clank" games for 14 years, Munroe believes the movie has a universal appeal.

"It was just about trying to create clever moments that if people weren't fans, they could at least see the humanity in it," he said. "But ultimately it can't be afraid of what it is, which is a sci-fi family adventure. If that's what it is, embrace it, because you're just going to mess it up if you don't."

"Ratchet & Clank" opens Friday nationwide.