The contemporary soundtrack market, studio execs say, has collapsed. The album for “Titanic,” until recently the most popular movie in history, sold 28 million units; “Avatar,” from the same filmmaker and composer, and which has surpassed “Titanic” at the box office, has sold about 100,000.

And yet the business of marketing movie music from 30 or 40 years ago is booming. In the past few months, film music aficionados have been able to buy — for the first time — John Williams’ score for “Black Sunday,” Bill Conti’s Oscar-winning music for “The Right Stuff” and Jerry Goldsmith’s “Players.”

A handful of small California-based labels are now releasing about 150 albums a year of classic (and sometimes not-so-classic) music from, mostly, the ’60s, ’70s and ’80s. It’s estimated to be a $10 million business annually, and all are thriving.

“It’s a great time for collectors,” says Douglass Fake, owner of Oakland-based Intrada Records, which is releasing nearly 50 albums a year, mostly catalog material. “Never before could they see all sorts of things they never expected: Alex North, Bernard Herrmann, reissues, expanded editions, newly recorded classics, you name it.”

These scores appeal to a niche market of 3,000-5,000 film music fans worldwide. Most are mail-order “limited editions” of 1,000 to 3,000 units, although some sought-after scores (“Back to the Future,” “The Goonies”) merit a 5,000- or even 10,000-unit pressing.

“There are about 1,000 fanatical collectors who have to have everything,” notes Bruce Kimmel, a veteran producer who now runs the boutique Kritzerland label, which recently released and immediately sold out of 1,500 copies of “Love With the Proper Stranger.”

This recent bonanza of classic titles is, for the most part, the result of lower rates charged by the American Federation of Musicians for the use of music recorded by its members. Studios pay them once to record a film score, but when that music gets a second use on a soundtrack album, they’re paid again — and until recently, they were paid at their full original rate.

“It just wasn’t feasible for an archival project,” explains Varese Sarabande producer Robert Townson. “In order to do a score from 1950, you were paying exactly the same rate as something recorded last week. It could easily become a six-figure deal. These days, it’s not possible to support that.”

Over the past 20 years, the AFM has gradually modified its rate structure to allow for what it calls “historical releases” — $1 or $2 per disc depending on the age of the recording, with total sales capped at a specified few thousand and the added proviso that the album include the AFM logo and the names of all the musicians who played on the score.

The number of soundtracks released over the past five years has probably quadrupled, says AFM Local 47 vice-president John Acosta.

And, while some union members aren’t happy about the reduced income, others view it as an acceptable trade-off — an ongoing advertisement for scoring in L.A.

From the studios’ viewpoint, “it’s a win-win for them, and for us,” says La-La Land Records president Michael Gerhard, who has projects brewing with Fox, Paramount, Warners and Universal. “We transfer everything, master everything, hand them back a digital copy and pay for it all. They get an advance plus royalties, and they retain all digital rights.”

Advances, say insiders, range from $2,500 to $10,000 and in rare cases (usually high-profile projects) $25,000 or more. More significant is the digital restoration that becomes a studio asset capable of generating more income — via DVD or Blu-Ray use, digital downloads or subsequent licensing for other purposes.

Label execs point to Fox as the leader in score restoration, initially for its own, short-lived record label in the early 1990s.

The studio has restored more than 700 of its scores — most of which were recorded on optical film, then magnetic film, long before tape became the recording medium of choice — with another 300 in the works, according to studio music consultant and producer Nick Redman.

The result has been new albums of Fox classics ranging from “Laura” and “The Day the Earth Stood Still” to “Planet of the Apes” and “The Poseidon Adventure,” all sought-after by collectors. Film Score Monthly’s Lukas Kendall says that Williams, Herrmann and Goldsmith are fan favorites.

Multi-disc sets, often pricey, are also popular. Kendall’s 200-plus releases include an 8-disc box of “Superman” scores ($120), a 15-CD Miklos Rozsa box featuring “Quo Vadis” ($180) and a 12-disc box of Elmer Bernstein-conducted classics including “To Kill a Mockingbird” ($200). La-La Land is preparing a 4-disc set of “X-Files” music.

But, suggests Kendall, the days of physical product still desired by the fans (who like the colorful booklets and detailed notes) may be numbered.

“As iTunes becomes more the default way to listen to music, the studios will make it a matter of course to see that their music archives are digitized,” says Kendall. “You will always have new generations discovering this music. It’s just that the delivery mechanism and business model will change.”