“We can’t do anything in marketing without music. It’s the driving force for everything,” says Ann Mugglebee, president of Vibe Creative, a Culver City-based agency that specializes in producing trailers and TV spots for movies.

Music for trailers has evolved from the use of score directly from the film being promoted (as in studio-produced previews for “Casablanca” or “2001”) to a highly competitive business in which composers create libraries of original music for the sole purpose of driving audiences to new movies.

“When we get a job,” says Mugglebee, “the first go-to is the music. There’s always a lot of pressure to find the right cue. Most of the time, for editors, it starts with the music.”

Studio marketing departments now outsource trailer creation to several companies that specialize in selling films. They then turn to either production-music libraries or, increasingly, to boutique music suppliers whose primary job is to compose, produce and promote music created specifically for what used to be known as “coming attractions.”

Most of the time, the composers of this music never even see the visual content. “They used to send me the cut and I’d just score it,” says Veigar Margeirsson, the Iceland-born composer whose L.A.-based Pitch Hammer Music specializes in trailer music. But too many leaks have resulted in high security and they now supply music based on suggestions and ideas from the trailer-producing companies who hire them.

Pitch Hammer creates about 100 new tracks a year, categorizing them as “emotional drama,” “percussive action,” “aggressive action” and a new, sound-design-based, non-tonal music they call “trailer fuel.”

“Music sets the tone,” agrees Bobby Gumm, head of music for Trailer Park, a Hollywood-based company whose recent trailers include “Captain America: Civil War,” “Zootopia” and “Finding Dory.”

Covers of classic songs are still in vogue, depending on the project. For the upcoming “Suicide Squad,” Gumm hired Confidential Music’s John Hanson to come up with a cover of the Bee Gees’ “I Started a Joke.” And it was Gumm who suggested Verdi’s Requiem for a “Mad Max: Fury Road” teaser – a classical-music choice that wound up in the movie itself. “I was ecstatic,” he admits.

For “The Jungle Book,” Vibe approached The Hit House, which created a cover of the classic song “The Bare Necessities.” “What we do is, we make you feel,” says Hit House exec producer Sally House. “We make you laugh, we make you cry, we make you go call your mom. (For “Jungle Book”) we knew that we had to make you feel inspired.”

And when they want to use master recordings (the original hit records), even then there is additional tweaking. House calls their approach “trailerization: some sweetening, overlay or sound design, (often) to end with a huge sweeping arc at the end.”

Music budgets for trailers can vary widely, from $5,000 to $2 million (the higher numbers generally reflecting the use of a top artist like Jay Z or U2).

A surprising aspect of today’s trailer music is the fact that few trailers sport a unified, cohesive score by a single composer. “They typically don’t use a full track,” says Margeirsson. “They’ll use two seconds of one track, three seconds of another, maybe 30 seconds of another, and maybe a track from one of our competitors.”

Rare exceptions involve the film composers themselves contributing. “On the Batman movies, Hans Zimmer would send us stuff piecemeal as he was composing it,” notes Gumm. John Williams provided music for the “Harry Potter and the Sorcerer’s Stone” and “Star Wars: The Force Awakens” teasers; Michael Giacchino scored trailers for “Ratatouille” and “Star Trek.”

“Trailers are like the last great frontier for music,” says Hit House composer Scott Miller. “They just keep pushing the limits. They don’t really want yesterday’s music, they want tomorrow’s music. You cannot think big enough.”