Meet Captain Cuts, the L.A. guys who mashed up Paramore and Selena Gomez

Fetty Wap and Blink-182. Drake and Say Anything. Justin Bieber and Fall Out Boy.

At a moment when the Internet has hastened the erosion of traditional genre lines, the idea of a pop idol or a rapper teaming with an emo band isn’t as hard to imagine as it once might have been. But just because something can be envisioned doesn’t mean someone has actually done it — at least in real life.

Give thanks, then, to Captain Cuts, the Los Angeles trio that gives virtual life to those fantasy-league collaborations on “If You’re Listening It’s Never Too Late,” a delightful new mixtape that mashes up songs by today’s chart stars with yesterday’s drama kings. Posted last month on the free streaming site SoundCloud (where it quickly racked up more than a quarter of a million plays), the half-hour-long set conjures fond memories of a not-so-distant past — no surprise, given that it grew out of Captain Cuts’ regular DJ gig at Taking Back Tuesday, a popular L.A. club night catering to emo fans who came of age in the early to mid-2000s.

Yet the mixtape is more than a millennial nostalgia trip. It’s also a savvy demonstration of musical understanding that peaks when the trio seamlessly matches the yelping vocals from the All-American Rejects’ “Swing, Swing” to the pulsing electronic groove of “Where Are Ü Now,” the ubiquitous 2015 banger by Jack Ü featuring Bieber.

“At the time, the emo stuff wasn’t really for the mainstream,” said Ben Berger, one-third of Captain Cuts, along with Ryan Rabin and Ryan McMahon. “It was something for the kids in the scene to hold on to and kind of build a community around. But when you listen back, it’s clear these guys were great pop songwriters. The melodies are hit melodies.”

Berger should know: When they’re not revising guitar-band history, the three (all between ages 28 and 30) work as freelance writers and producers in L.A.’s busy pop-music industry. Last year they scored a top 5 single with “Shut Up and Dance,” by Walk the Moon, and co-wrote and produced “Roman Holiday,” a cut from Halsey’s “Badlands” album, which entered the Billboard 200 at No. 2.

Like virtually everything on Top 40 radio, the Captain Cuts sound is slick and precision-geared. Yet Berger said their goal isn’t merely to impress other producers with their programming skills. “Cool but approachable,” he called it, adding, “We want our music to be something that a kid and their mom can both enjoy.”

The three met as students at Harvard-Westlake School, where they played in various bands and learned to record themselves using hand-me-down equipment from Rabin’s father, the producer and film composer Trevor Rabin. After going to separate colleges, they reconvened in L.A. around 2010 and started writing together “almost as a joke,” Ryan Rabin recalled as he sat behind a mixing board in the trio’s cozy North Hollywood studio.

“We were like, ‘Should we just try to make a funny Miley Cyrus song?’ ” he said.

“At first you think it’s going to be easy,” added McMahon. “Then you find out it’s actually really hard.”

Honing their abilities in part through work with Grouplove, the rock band in which Rabin plays drums, the producers kept at it and eventually won the attention of publishing companies and record labels. Now they’ve built songs for acts such as Tove Lo, Sabrina Carpenter and the squeaky-clean sibling outfit R5.

Jeremy Vuernick, an A&R executive at Halsey’s label, Astralwerks, said that Captain Cuts’ specialty is helping artists give shape to fanciful concepts, just as the trio did with its alternate-universe mash-ups.

For “Roman Holiday,” Vuernick said, Halsey “went to them with a landscape she wanted painted — something kind of vintage-feeling — and they took her vision and put it to sound.

“And these are guys,” he added, “who’ll work till 8 in the morning to get it right.”

They were no less dogged making “If You’re Listening It’s Never Too Late,” whose title is a riff on the name of a 2015 record by Drake. (As the result of a complaint from the rapper’s label over the use of his vocals, the Captain Cuts mixtape was recently removed from SoundCloud but is now streaming on YouTube.)

To find instrumental parts and a cappella vocal tracks, many hacked from the Guitar Hero and Rock Band video games, the three searched “the deepest crevices of the Internet,” said McMahon. Then they assembled a spreadsheet listing the key and the beats per minute of each song they wanted to use and started lining up tunes to see which ones fit.

“This makes us sound like the biggest losers of all time,” Berger said with a laugh.

Yet every time they landed on a killer combination — DJ Snake with Dashboard Confessional, or Paramore with Selena Gomez — “we knew we had to keep going,” said Rabin.

Earlier this month Captain Cuts brought the music back to its spiritual home for a jampacked party celebrating Taking Back Tuesday’s one-year anniversary. The club night is scheduled next for Feb. 2 at the Echoplex in Echo Park.

“It’s so fun,” Berger said of watching a room react to an unexpected pairing. It’s good advertising, too.

“Since we started doing this, we’ve had several people reach out,” said Rabin. “They’ll say, ‘Oh, my God, this is amazing! Can we do a session for, like, a real thing?’ ”

mikael.wood@latimes.com