Will Smith never used to worry if his movies "sucked" - so long as they had good trailers.

Will Smith

Will Smith

The 50-year-old actor admitted it used to be much easier to make a popcorn blockbuster because it took a while for people's verdicts on the films to come in, but the instantaneousness of social media has forced change because now a strong promotional clip is no longer enough to drive audiences into cinemas.

He admitted: "We used to say 'We're not in the movie business, we're in the trailer business.

"Once you have a good trailer you're done. Now, what's happened with technology, on Friday night at 7:30, people are tweeting, 'Hey Will's movie sucks, go see Vin Diesel's.'

"We no longer [have] the three-day window. If you had a great trailer, it was Monday at noon before everybody knew that 'Wild Wild West' sucked. You had already made your money. 'Oops, sorry, catch you on the next one.' "

He also recalled speaking to a producer about the way technology has changed.

The executive told him: "This is bulls**t. We got to make f***ing good movies now."

But the 'I Am Legend' star - who has son Trey, 25, with first wife Sheree Zampino and Jaden, 20, and Willow, 17, with wife Jada Pinkett Smith - wouldn't be surprised if people chose to see Vin Diesel's movies over his own.

He quipped during a talk at New York's Advertising Week: "Vin is sexy. Vin is a sexy man."

After successful ventures into acting, rapping and producing, Will has now become an online sensation thanks to his popular YouTube channel and he's pleased with his new direction.

He said: "I feel like I'm getting a fourth bite of the entertainment apple."