The science of the trailer

We're in the middle of another summer of blockbuster movies. But despite the success of the finale of the Harry Potter series, and the pleasingly non-jingoistic exploits of Captain America, it's been an uninspiring, mainly imagination-free slate typified by Michael Bay's poor Transformers: Dark of The Moon.

Jeffrey Katzenberg, a founder of DreamWorks, even referred to the past seven or eight months as "the worst line-up in five years".

It's no wonder then that the attentions of filmgoers are turning to a raft of teaser trailers for 2012's hoped-for megahits, including The Amazing Spider-Man, Judge Dredd's comeback in Dredd and Christopher Nolan's third and final Batman film, The Dark Knight Rises.

"Teaser trailers can be launched up to a year ahead of release," explains London-based publicist Rupert Fowler, who began his career in LA and has worked on many film campaigns. "Nearer to release there can be as many as five different versions, varying in length and concentrating on specific characters or themes, such as romance, suspense or action."

Trailers are a major part of a movie's marketing drive. They can ensnare: The Tree of Life trailer is a visual treat hinting at an intense character-led drama but does little to prepare viewers for the sparse dialogue and 20-minute evolutionary in-film montage.

They can tell you little but be slick, dramatic and enticing: the US version of The Girl With the Dragon Tattoo has no dialogue or voiceover and is simply cut to the rapid beats of Trent Reznor and Karen O's cover of Led Zeppelin's "Immigrant Song" ("it does a superb job of drawing you in," says Fowler).

They can also be poor. Early trailers for The Adventures of Tintin had fans chewing their nails in nervous frustration until later ones eased the character out of the shadows and laid on the action.

Above all, they are crucial to get right. "First impressions count. A poorly-received trailer can result in much money spent and many hours fretted working to turn opinion around ahead of release," says Fowler.

The trailer came into being in 1913 when the Loews Cinemas company created one for the musical, The Pleasure Seekers, which was playing on Broadway. But the early days of trailers were usually maladroit and audiences immediately knew they were being sold something. The Bishop's Wife in 1947 gave a knowing nod to such tactics with a self-referencing trailer staring David Niven and Cary Grant on their way to film a promo for the movie.

Until the 1950s, American trailers were produced by the National Screen Service, although some directors such as Alfred Hitchcock and John Ford liked to produce their own. In the 1960s film directors took a keener interest, leading to more stylish trailers. Plot spoilers in trailers still existed into the 1970s although trailers were less brash than today. "This is Universal's extraordinary motion picture version of Peter Benchley's best-selling novel, Jaws," intoned the gentle voiceover on a trailer for Speilberg's shark fest which, during its three minutes, showed so much footage and dialogue, it was akin to an abridged version of the film.

By the 1980s, trailers were more vague and teasing. Today, producers of trailers understand they are not selling a narrative but an abstract representation of one. They tend to make films seem like an offering ("the producers of Film X bring you...") and they stick to strict time limits of two minutes and 30 seconds as laid down by the Motion Picture Association of America.

"Fractions of a second make all the difference in whether a joke 'lands' or doesn't or whether a montage builds to the right climax or whether a drama trailer just plays," says trailer editor Mark Woollen, who has worked on promos for The Tree of Life, True Grit, The Social Network and Black Swan.

Trailer editors work to a script that reflects the direction and style of the overall campaign. Sometimes they are given raw footage and wade through dozens of hours of film, attempting to boil it down to around 2,880 frames.

"There are plenty of bad trailers that are cliché-ridden, have cheesy voiceovers, and are misleading or reveal too much," says Woollen. "And yes, there are a lot of trailers that follow a three-act storytelling structure, and build to an escalating climax. Great trailers are always about raising questions but never answering them, and about whetting your appetite. When you can remember the trailer after the film you've seen, that's often the sign of a good trailer."

Since trailers are all about pacing and rhythm, the right piece of music is important (although quite a few plump for composer Clint Mansell's "Lux Aeterna", written for Requiem For A Dream but used on trailers such as The Da Vinci Code, Sunshine and I Am Legend).

"Music is everything," says Woollen, who cites the use of Radiohead's "Creep" in The Social Network as an important part of setting the tone for the trailer. It's rare a film's actual score will appear in a trailer since the movie is rarely finished by the time the trailer is edited. Many use music composed for other movies and there are banks of pre-recorded tunes.

"Trailer companies also use music supervisors who review music and provide it to producers and editors," says David Malki, who has edited trailers for Michael Moore's Uprising and Thank You for Smoking. "This can include bands and labels that want their songs featured."

Let us not forget, too, the gravelly tones of the voiceover, which is nearly always a man. "A male voice brings a sense of authority and gravitas," says Malki. "I don't know what this implies about us culturally. TV adverts are much more egalitarian."

Some trailer producers like to steer away from voiceovers. "I prefer to have the movie's characters and dialogue tell the story," says Woollen. "A couple of strong lines of dialogue or voiceover from a character can really set-up the premise."

Another trick is the montage. Trailer editors look for iconic, easily read images that have strong emotional visceral impact and stick in the memory. Fast cuts make even the most turgid of movies appear exciting.

Over the years, trailers have been seen as worthy of study. "They play on emotional impact, set up situations, and produce an overall feel, both aesthetic and emotional, very quickly," says film expert Dr Kriss Ravetto-Biagioli, of Edinburgh University.

And some can be better than the films. "George Lucas' Star Wars prequels were lousy but the trailers were incredibly stylish and expressive," says Daniel Hesford, who is writing a thesis on the subject. "They used minimal percussive soundtracks, musical cues from the famous score, skilful montages and the best, most expressive and aesthetically spectacular shots from the films themselves."

Trailers have also become the subject of gongs. The Golden Trailer Awards were set up 12 years ago by sisters Monica Brady and Evelyn Brady-Watters. The popularity of Apple's Trailers site, which allows film fans to download HD clips, attests to how much fans value what are essentially adverts for products. "When you add up all the numbers, it's close to a $200 million industry when it comes to the cost of making these trailers," says Brady.

In the future, trailers will become more engaging. Not content with eye-catching mini-movies attracting the hits on YouTube, studios want interactivity. Woollen owns i-Trailers, which produces trailers that allow viewers to discover more information and behind- the-scenes footage. "Audiences can now engage with a trailer for up to an hour," he says. "A good trailer is all about seduction. It should tease you, make a strong impression, and then leave you wanting more."

Film snapshots: Movie trailer editor David Malki casts his eye over some recent movie promos

The Adventures of Tintin

It's clear that the advertisers knew they had to work around the creepy CGI people. You almost never see any faces at all until the very end, and even then it's very brief. Heavy on the spectacle and the "huge set pieces you've never seen before", which is always a big thing for action trailers.

Green Lantern

The first Green Lantern showed Hal Jordan discovering the ring and his powers and was human-centric. This second trailer is clearly aimed much more at the fans. There are a lot of alien and space shots without being afraid that it is too weird for the audience.

Horrible Bosses

Listen closely to the choppiness of some of the lines. "I have decided who I want to be our new vice-president" has been edited together from longer lines, or lines with more pauses, or lines from other parts of the scene in order to communicate the story beats. Anything that made test audiences remotely laugh made it into this trailer.

Sucker Punch

This must have been fun to cut. Give me a movie like this to work on over a serious, wonderfully-paced drama any day. I worked on a great movie where everything was shot in long, intense takes. It was impossible to make an interesting trailer.

Twilight

This teaser only serves one purpose: to let fans know that there's going to be a movie and in it, Edward is going to be hunky. It's really drab and sedate if you're looking at it objectively.