The BBFC already issues ratings for games aimed at adults
Age ratings for downloaded video content and video games are to be introduced in the UK.
Overseen by the British Board of Film Classification (BBFC), the scheme will see certificates appear on websites, via set-top boxes and portable players.
Disney, Warners and Fox have signed up to the scheme with other "key industry figures... poised to join the scheme".
The BBFC said independent research showed 74% of parents were concerned about the lack of ratings on downloads.
More than 1,000 videos will have online certificates by the end of May.
The voluntary scheme will also require online services and video on demand schemes to have "age verification or gate-keeping systems in place for parents to monitor and control underage viewing".
Peter Johnson, head of policy at the BBFC, said the body would police the age verification systems.
"It's up to individual systems to work out how to introduce these technologies," he said.
"But we will police it through test purchases."
Mr Johnson said the scheme, called BBFC.online, was not an attempt to censor the internet, nor to regulate online video gaming.
David Cooke, director of the BBFC, said the organisation continued to work with the game industry's self-regulatory body Pegi to find solutions to classifying the burgeoning range of online gaming.
The BBC could enter iPlayer into the scheme
"We don't need to set up in rivalry with Pegi online. We can work cooperatively," he said.
The scheme could also be rolled out to include online services such as Microsoft's Xbox Live, Sony's PlayStation Network and Nintendo's WiiWare, all of which offer video and games for download.
While the BBFC system has not been designed with TV catch-up services, like the BBC's iPlayer, in mind, said Mr Johnson, organisations like the BBC and ITV were welcome to join.
Without providing specifics, Mr Johnson said the BBFC expected all the "leading content providers and aggregators to sign up to the scheme in the coming weeks and months".
"We are talking to everybody who is likely to be a significant player in this industry," he said.
Mr Cooke said he hoped the voluntary scheme would obviate the need for any legislation to cover downloadable video content in the UK.
The BBFC reported that parents it had consulted had expressed surprise that online video content did not legally have to be classified in the UK.
"I'm hoping there won't be any need for legislation to underpin this scheme," he said.