Given the comparative lack of dialogue, pornographers and triple-X movie stars of the San Fernando Valley have been unaffected by the screenwriters' strike crippling Hollywood's movie industry. But that does not mean all is going smoothly.

America's adult entertainment workers claim their $13bn industry is in trouble. Sales are down by as much as half as customers learn that what they once paid for can now be free. Pirated pornography is flooding the internet while thousands of 'amateurs' post their activities on websites such as YouPorn.

Last week, Vivid Video, one of the largest porn studios, took legal action against Pornotube, a website the company claims is depriving the industry and its performers of legitimate revenue by allowing the streaming of copyrighted material.

According to surveys, sites such as YouPorn and Pornotube draw more internet traffic than CNN. Like YouTube, the phenomenally popular, Google-owned website, X-rated sites depend on users streaming videos to the site - and YouPorn is adding 15 million new users a month.

'The adult entertainment industry is starting to get aggressive,' says Farley Cahen, an editor at Adult Video News. 'The problem is that more and more people are finding out about these sites and that they can get this free content.'

After a decade of double-digit growth, the porn industry is seeing sales of DVDs - its biggest money-maker - slip. Last year, total sales were down 15 per cent. The industry says it is laying off workers.

'Some people say porn is porn is porn, but consumers have preferences,' says Cahen. 'Some like amateur, with neighbours in their socks in a poorly-lit setting.' But 'most consumers like a more polished product with high quality production and prettier girls doing fun things'.

YouPorn is a mysterious entity. There is no contact information, no hint of where it is based. A man claiming to be the owner named 'Stephen Paul Jones' told Portfolio magazine that he was 27 and worked at a California hedge fund, where he managed billions in assets.

He claimed the site was not intended to make money: 'If you wanted to be philosophical about it, it's kind of an exploitative industry and this is sort of the opposite.' It is more probable that YouPorn is owned by Zach Hong, a Malaysian businessman who lives in Australia and is thought to be looking to sell it.

Regina Lynn, Sex Drive columnist for magazine Wired, says the easier it becomes for people to make and distribute their own content, the more they will do it. 'Despite social and professional stigmas, a lot of people are putting themselves on the internet. It fits into this era of people expressing themselves,' she said.