Giantscreens are almost as common as string sections in classical orchestras these days, as live movie concerts become an increasingly regular (and increasingly profitable) piece of programming around the country. And when you go to one of those concerts in Hollywood, you might just find the orchestra is conducted by one of the film’s original musicians.

That’s the case with “E.T.” when the concert screening of the film plays Sept. 4-6 at the Hollywood Bowl. Conducting the L.A. Philharmonic will be David Newman, a film composer (“Ice Age”) who was in the orchestra that recorded the John Williams score for Steven Spielberg’s 1982 favorite.

In New York, meanwhile, an October film concert of “Back to the Future” — produced, like “E.T.,” by Film Concerts Live!, a joint venture of performing arts management company IMG Artists and music talent agency Gorfaine/Schwartz — will feature some 20 minutes of new music that the film’s composer, Alan Silvestri, wrote specifically for the live-concert screenings.

“The music that’s there is fabulous, but there’s really only about 38 minutes of orchestral score in the film,” says Gorfaine/Schwartz’s Jamie Richardson, who oversees Film Concerts Live! with IMG’s Steve Linder. “So we nervously went to Alan and Bob Zemeckis and the screenwriters, and asked for more — and they loved the idea.”

FCL’s slate also includes “Raiders of the Lost Ark” and the two most recent “Star Trek” films. One of the company’s most popular titles is “Home Alone,” which has become a holiday hit for the promoter. There are 18 concert screenings on the books around the country between Thanksgiving and New Year’s.