Anurag Kashyap’s Bombay Velvet  had a nightmare opening weekend, the kind that would spook the producer of any film with a stated budget of Rs 80 crore and a rumoured budget of upwards of Rs 100 crore. Trade analysts estimated weekend collections in the region of a paltry Rs 16 crore, as opposed to a projected Rs 45 crore,.

Many reasons have been given for the indifferent response to the period movie set in 1960s Mumbai, starring Ranbir Kapoor and Anushka Sharma as star-crossed lovers, and co-produced by Phantom Films and Fox Star Studios: the enormous budget would always have been difficult to recoup, composer Amit Trivedi’s soundtrack didn’t fly, the Mumbai setting and English title made it difficult for audiences beyond Maharashtra and Gujarat to identify with, and the word of mouth seemed to match the tone of the reviews (middling to trenchant).

But Kashyap’s most complex production till date arguably lost a small part of the battle even before it opened ‒ at the time the producers released the trailers. They failed to whet the appetite and sent out confused signals about Bombay Velvet’s themes.

Trailers, which create curiosity and excitement about upcoming releases, are highly valued in an environment where hype fuels box-office success. The publicity blitz that surrounds a movie isn't restricted to the trailer, of course: it includes extensive media coverage (a great deal of it paid for), marketing campaigns, product placements and increasingly, a digital push on social media. The connection between a strong trailer and a film's popularity is a guessing game rather than an exact science, but it is possible to hazard a few generalisations.

The first peek into a movie’s universe ‒ usually, a poster or a set of photographs, followed by a few minutes of footage ‒ helps create “buzz” or interest and decides the scale of the release.  Sometimes, expectations do not match execution (as was the case with this year’s Shamitabh and Detective Byomkesh Bakshy!) Well-cut trailers tease out a movie’s major plot points without giving too much away (Baby, Badlapur, NH10) and give sufficient notice of the fictitious world that directors and their crews have created (Dum Laga Ke Haisha, Hunterrr, Piku, Dil Dhadakne Do.)

Given the fixation with marquee names within the trade as well as among cinemagoers, the mere presence of a star can make a trailer’s actual content irrelevant (as any Salman Khan title proves). Smart trailers for movies like PK play down potentially incendiary angles and emphasise the filmmaker’s core strengths (ability to handle social issues with lightness and humour, showcasing of star talent).

A smart trailer can go some way in helping audiences decide whether the package of stars, songs and whatever else the movie contains is attractive enough to flock to the cinemas. Is that why some trailers, such as the one for the upcoming Hamari Adhuri Kahani, give away the entire plot?

What’s left to watch in Hamari Adhuri Kahani, directed by Mohit Suri and based on a story by Mahesh Bhatt? Perhaps, there is still some curiosity in seeing a woman having an extra-marital affair for a change, Vidya Balan in an author-backed role, and Emraan Hashmi as support system rather than homebreaker.

Sometimes, a trailer works like an advance warning system. After watching the snappy summation, potential ticket buyers might decide that it isn't worth reaching for their wallets this time (Broken HorsesMr X). After that, no amount of favourable reviews can persuade the viewing public to make their way into the cinema hall. If reviews could directly translate into box-office receipts, then Chaitanya Tamhane’s arthouse gem Court would have been this year’s biggest hit.

Is the trailer supposed to tease or reveal? How much in advance should a film be exposed? Two months or three? Six? Does the enthusiasm of the twitterati who live in the corner of north Mumbai where the movie business is headquartered translate into popularity with audiences? Conversely, do the forecasts of trade analysts, who make predictions about audience behaviour every Friday (this movie will run only in the smaller centres, this other one is meant for the non-resident Indians) continue to have relevance at a time when viewers have become much more sophisticated?

Trailers serve a vital function: they build a bridge between art and commerce. But if the foundation is weak to begin with, there is only one direction in which a movie will head: the bottom.