Forget watching trailers before a feature film – previews are now the main event.

The online video touted an epic unveiling from one of Hollywood’s most revered filmmakers: ”In three days, Ridley Scott returns to the genre he redefined.”

For the next two days, videos ratcheted up the excitement for the new project. Finally, it arrived: not the movie, not even the full-length trailer, but the one-minute ”teaser” for Scott’s upcoming film Prometheus.

”We teased the teaser,” says Oren Aviv, the chief marketing officer for 20th Century Fox. ”And it was viewed 29.7 million times.”

This is the new world of trailers, in which the internet and fan culture have turned one- to three-minute ads, once seen only in cinemas, into events promoted and analysed as avidly as the films themselves.

Trailers are now watched more online than in theatres. Audiences streamed more than 5.3 billion trailers worldwide last year and are on track to significantly outpace that figure this year.

”Our work used to be looked at as pieces of advertising that quickly comes and goes, but now it’s a key piece of content that people are going to analyse and judge,” says Michael McIntyre, the president of a Los Angeles entertainment marketing firm mOcean, which has made trailers for films including The AvengersProject X and The Grey.

Aiming to take advantage of the mania surrounding trailers, studios now market the marketing. Movies that followed the Prometheus lead, with a ”trailer for the trailer”, have included The Twilight Saga: Breaking Dawn – Part 2 and Total Recall, and Sony Pictures held screenings in 13 cities around the world in February to debut a trailer for The Amazing Spider-Man.

The likes of Yahoo and iTunes battle to be the ”exclusive” first home for a trailer online, often trading high-profile placement on a home page in exchange for the favour. In other cases, trailers are shared with devoted fans via Twitter or Facebook. Sometimes studios pay hundreds of thousands of dollars to companies promising to help turn videos viral.

”You used to put the trailer in theatres and hope for the best but now we can use digital marketing tools to make it a destination,” says Marc Weinstock, the worldwide marketing president for Sony.

First used nearly 100 years ago and shown after the main feature, trailers long consisted of scenes from a film interspersed with text or narration. Eventually they evolved to feature super-fast cuts, flashy graphics and original soundtracks.

Studios spend between $US100,000 ($97,000) and $US200,000 to make each one, though costs can hit $US1 million if the trailer includes an expensive song.

To keep fans engaged and take advantage of the web’s endless inventory, studios now put practically every available piece of content – be it trailer, commercial, clip or behind-the-scenes feature – online.

”We get so many more assets and they’re rolled out earlier and earlier,” says Sybil Goldman, the vice-president of entertainment for Yahoo.

The increasing number of trailers online means increased scrutiny for the people who make them. Bloggers and tweeters dissect every frame of a trailer for mysterious projects, such as The Hunger Games or Prometheus, and can create instantaneous bad buzz for films whose trailers they don’t like, as happened to the flops John Carter and Green Lantern.

”People have access to so much marketing content in so many ways now that you have a higher bar for what is and isn’t a good trailer,” Aviv says.

There’s also growing scrutiny of the campaigns themselves. Avid fans are aware of the huge amounts of content being thrown at them and are becoming increasingly cynical.

”The general consensus among people I know is that they are milking it too much with a trailer for a trailer,” says Nick Bosworth, the editor of the trailers section on the movie fan site JoBlo.com.

Critics also complain that trailers can give away the whole film. But testing shows that moviegoers are less likely to buy a ticket when they don’t know what to expect. Studios, in other words, are sticking with what works. As the hype and attention around trailer debuts keep growing, they increasingly resemble another high-stakes moment for the movie industry.

”In some cases,” says Mojo co-owner Michael Kahane, ”the trailer launch has become just as big an event as the movie opening weekend.”

Los Angeles Times