About 200 pornographic films are shot in the US every week

The scale of the Adult Entertainment Expo reflects the huge growth in a business which is said to be bigger than Hollywood and worth $57bn (£29bn).

Estimates of its annual contribution to the US economy range from $12bn-$20bn.

One of the reasons for its recent success is the pioneering use of new technology - video on the internet and use of moving images on mobile phones.

The BBC's Guto Harri in Las Vegas says it is easy to be embarrassed at such a show, with explicit films, intimidating toys and hundreds of half-naked actors on display.

The adult industry is bigger than every professional sports combined - it's part of life, it's mainstream now

Adult entertainment model

Jasmine Mai

But the scale and seriousness of the convention is not that different to a more mainstream gathering because pornography is big business, our correspondent says.

Adult entertainment model Jasmine Mai told the BBC: "The adult industry is bigger than every professional sport combined. It's part of life - it's mainstream now."

'Innovations'

Embracing new technology has been critical to the industry's development, and has allowed people to access it more easily and more discreetly, bringing in new customers.

Adult entertainment helped determine the dominance of VHS over Beta, it was crucial in the development of video on the web, and is now pioneering moving images on mobile phones.

There are an estimated 200 pornographic films shot in the United States every week. Improving production and distribution methods has helped to cut costs.

Our correspondent says many people regard pornography with disgust, but mainstream entertainment has and will continue to benefit from the technical innovations of the shameless people who are in Nevada this weekend.