VIRAL: The first season of YouTube musical 'Side Effects' drew 2 million views in a week. AwesomenessTV

Like so many other YouTube hits, "Side Effects" has singers covering tunes that were first made famous by pop stars. What makes this project different: The Taylor Swift and One Direction covers have been stitched into an original story line featuring a dozen actors, extensive visual effects and a total running time of 80 minutes—an epic production compared with typical viral videos.

"Side Effects," about the family mystery surrounding a teen who hallucinates song-and-dance numbers, highlights the rise of musicals on YouTube, where Broadway (or at least TV's "Glee") is exerting a growing influence.

So far this year, people have uploaded 13,200 hours of video with "musical" in the title, compared with 9,700 hours during the same time last year, YouTube says. The spread of theatricality online has happened in step with the popularity of big-screen musicals such as "Frozen" and "Pitch Perfect," a teen favorite from 2012 that is set for a sequel.

Web musicals also show how the homegrown culture of YouTube is evolving. Creators are looking for new ways to get noticed within the never-ending glut of cover songs and lip-sync videos, long favored by people pursuing Web stardom. Now, some musicians are winning big audiences with their original compositions.

In "Side Effects," five siblings grappling with the death of their mother and a home foreclosure follow a trail of clues in search of their vanished father. As a reaction to the medication she's taking, middle child Whitney (Meg DeLacy) sees her and her family's emotions come to life as music videos, giving the characters an excuse for breaking into songs from Kesha and "Pitch Perfect" and others. Overseen by director Matt Stawski, the musical interludes feature animation and different styles of effects for each character.

The musical has some star power. Chester See, a singer with 1.5 million YouTube subscribers, plays the role of the eldest sibling and stand-in father figure, Keith. He executive-produced "Side Effects" and co-wrote one of the musical's several original songs. The producers didn't need permission for the songs they cover: YouTube has a system that allows the songs' rights holders to either take the video down or share in any ad revenue it generates.

Mr. See, who says he's putting his UCLA theater degree to use, notes that "Side Effects" has a lot more in common with "Glee" than "Guys and Dolls," but notes the influence of Top 40 on the genre as a whole. "Look at the stuff popping up on Broadway—more of it is pop music," he said. For example, current offerings on Broadway include "Motown the Musical" and "Beautiful: The Carole King Musical."

The first "season" of "Side Effects" went online last fall as a single 42-minute video, which attracted 2 million views in one week, the producers say. A second season has rolled out in more typical fashion, in weekly episodes about seven minutes long, with the last installment appearing this week. A third and final batch of episodes will come out later this summer.

With a budget upward of $200,000 for the first season, "Side Effects" has some muscle behind it. It was produced by AwesomenessTV, a YouTube network that runs dozens of teen-focused shows. Last year DreamWorks bought the company, which also produces an AwesomenessTV series for Nickelodeon.

Like other hit YouTube videos, popular musicals generate revenue from ads that run automatically before the clips play. The goal for the "Side Effects" team, however, is to sell the show for TV. "We set out to make something that was more than just a YouTube video, something that could live on network television or cable," says Awesomeness founder and chief executive Brian Robbins. Mr. Robbins says he is in talks with a cable network about adapting "Side Effects" for television. Online, ambitious musicals aren't yet sustainable, he says: "Unless we had some other way of paying for it, it would be hard to make this show every week on YouTube as an hour or half-hour."

DISNEY VILLAINS: Brothers Antonius, left, and Vijay Nazareth with cast of their new musical AVbyte

Musicals, like most online productions, rely on Web searches to lure an audience. Two brothers in New York piggybacked on people's interests in big releases, especially from Disney, DIS +0.76% to introduce their own original music.

Knowing that the Angelina Jolie movie "Maleficent" was coming to theaters, Antonius and Vijay Nazareth recently created "Disney Villains—The Musical featuring Maleficent." Four women dressed as the antagonists of such movies as "Snow White and the Seven Dwarfs" and "The Little Mermaid," sing about their misunderstood good intentions. Chorus: "A happy ever after is a dream that won't come true."

Though their "musicals" consist of a single song—"Disney Villains" is three minutes long—Antonius says the brothers are "crazy passionate about bringing back the golden age of theater and musical films." Both siblings are classically trained musicians, but Vijay oversees the video production while Antonius handles the music.

In about a week, the video has gotten 1.4 million views, but it has a way to go before matching the 28.2 million views of their biggest hit: a musical riff on "Frozen." That video featured a girl-power anthem by a group of Disney heroines: "Who says every princess needs to have a prince. It's the same old story but I'm just not convinced," they sing.

Under the name AVbyte, the Nazareths have uploaded almost 200 songs (and behind-the-scenes videos of their musicals) in the last two years, spoofing everything from the Grand Theft Auto videogames to "Fifty Shades of Grey." The brothers declined to specify how much money their videos generate, saying only they earn enough to live in Manhattan without needing separate jobs.

Like the creators of "Side Effects," the Nazareth brothers want to take their musicals to a stage beyond YouTube. They recently got a manager and an agent, who have them working on movie ideas. "We're trying to build a musical brand," Vijay says. "That's why we made it a point to always stick to original songs, so we have a clear voice."