A few weeks ago, 5,000 people in London’s Royal Albert Hall cheered “Interstellar” after it unspooled with a full orchestra playing Hans Zimmer’s powerful score in its entirety.

This summer, the Hollywood Bowl will play host to tens of thousands more watching “Back to the Future,” “2001: A Space Odyssey” and “E.T. the Extra-Terrestrial” — all with live accompaniment by the L.A. Philharmonic. Films like “Psycho,” “The Wizard of Oz” and “Star Trek” are popping up on orchestra programs around the world.

After years of looking down their collective noses at film music as unworthy of performance alongside, say, Beethoven or Wagner, orchestras from the Chicago Symphony to the New York Philharmonic are jumping on the bandwagon, playing classic film scores “live to picture” in growing numbers.

“It’s gone from an occasional novelty to being a vital part of the concert-going experience,” says Brian Grohl, pops program manager at the Hollywood Bowl. “In an age when you can watch anything at home or on your iPad, you need a spectacular and unique element in your concert not only to attract new audiences but to keep the interest and excitement for the people who are already coming.”

Conductors, orchestra managers and producers agree that the technology has made it easier than it once was to keep musicians in sync with the picture (a vital element of film music dating back to the silent era) — but also that audiences are looking for “events” that combine music and visual spectacle.

“Orchestras love to do it because it brings in a big audience,” says Hollywood veteran David Newman, who has often conducted “West Side Story” and who will conduct “Back to the Future” and “E.T.” this summer at the Bowl, and “On the Waterfront” in September with the New York Philharmonic. “Orchestras understand they cannot survive financially without including everyone,” he says, especially younger audiences that might not normally attend a symphony concert.

“The music is really symphonic,” says “Live From Lincoln Center” creator John Goberman, whose Symphonic Cinema company produces “Psycho,” “Oz,” “Casablanca” and other film-with-music programs. “What better way to hear it than in the concert hall? If you’re going to play the original music from the film, the best way to hear it is with the form that dictated the structure of the music.”

The phenomenon actually dates back to 1987, when Goberman persuaded the L.A. Phil to perform Prokofiev’s legendary score to “Alexander Nevsky” live to the film. The “technology” was nonexistent: an orchestra librarian had to sit next to conductor Andre Previn and cue him before the start of every musical sequence.

The process today is easier but not easy, and it generally requires conductors who are accustomed to dealing with “click tracks” (a kind of digital metronome) and “streamers and punches” (visual cues that appear on the conductor’s TV monitor) that help keep them in sync with the music.

And that is just part of the work involved. The studio that owns the film must sign off on the idea, and if possible provide a print of the film that permits dialogue and effects to be heard but not the music.

Justin Freer, whose CineConcerts company does many of these events (including “The Godfather,” which played L.A. in January and “Gladiator” last year in London), will debut “Breakfast at Tiffany’s” with its Oscar-winning Henry Mancini score June 12 in London. Because Paramount recently restored the film, “all of those audio tracks are broken out individually.”
Also, Freer points out, the music itself needs to be adapted or modified for live performance. In the case of “Gladiator,” he spent weeks transcribing the multiple layers of percussion because so little of it had actually been written down. Then it was a matter of condensing the parts from 16 percussion players to a more standard four or five.

“How to preserve or interpret what the composer originally intended versus the very realistic problems you have once you start mixing dialogue, music and effects against one another in a live setting,” according to Freer, is always a looming question.

The initial cost to mount such productions can be “in the low six figures,” says one exec who has dealt with these issues. But the investment quickly pays for itself, most say — especially in cases like “The Lord of the Rings” films, which the 21st Century Orchestra of Lucerne, Switzerland, has performed more than 50 times since starting with “Fellowship of the Ring” in 2008.

Producer-manager Pirmin Zangerle says via email that their concerts “attract a wide audience: film music lovers, film lovers, young people, families.” The entire Swiss orchestra flew into New York earlier this month for six sold-out “LOTR” shows at Lincoln Center, with 250 musicians and choristers on stage.

They have also done “Pirates of the Caribbean,” “Star Trek,” “Titanic” and, on Dec. 4, will debut the John Williams classic “Raiders of the Lost Ark” (also in Switzerland, with U.S. dates to be announced later). As Newman quips: “You can probably book ‘Raiders’ and, when it gets done, ‘Star Wars,’ every weekend for the rest of your life.”

“It is a slow, steady rain of money,” says the exec who prefers to remain anonymous.

As for the musicians at the various orchestras tackling this music, Newman says, “orchestras are getting more and more accustomed” to playing film music. The key, he says, involves explaining the story and conducting it well.

“You have to find the thing that animates it,” Newman says. “ ‘Back to the Future’ is like a crazy clock ticking. It’s about movement. It’s almost balletic: the whole clock-tower thing, the skateboard scene, the storm and Doc coming down the wire.” Composer Alan Silvestri is writing 15 minutes of new music for the presentation.

The L.A. Phil “sees it as a broadening of their core audience,” says Hollywood Bowl director of presentations Laura Connelly. And the music, she says, is “part of the cultural heritage of Hollywood.”