The site, owned by AIM-listed firm Media Corp, is set to offer TV content, streamed radio and movies to consumers online in a bid to increase the time its 2.1 million unique users spend on the site.
The move is part of a drive to boost the profile of Onthebox and move away from being a provider of information to other sites.
Onthebox has benefited from broadcasters setting up video- on-demand services and streaming channels online. Keen to drive traffic to their sites, Channel 4 and ITV both currently have campaigns live on the site.
Sara Vincent, commercial director at Media Corp, said the plan for the site was to strike long-term partnerships with broadcasters to make ads relevant and unobtrusive. She also said Onthebox would continue adding multimedia content, as well as providing listings to users.
"The long-term view is to make Onthebox not only the place to come to gather information, but to communicate on forums, watch TV shows that you've missed and watch your favourite movies," she added.
Media Corp has recently added features enabling users to listen to digital radio through the site and plans to offer 25 radio stations for users to choose from. It has employed a team of copywriters to provide previews and reviews of TV shows and a round-up of soaps.
Vincent said the plans are under development and should go live within six weeks. Media Corp will also roll out a US version of the site, featuring listings for 200 TV channels, as well as cinemas.
Media Corp is funding the renewed investment with cash gained through the 2007 sale of Casino.co.uk, for which gambling firm Cryptologic paid up to £3.62m.
Media Corp owns a number of frequently visited sites including creditcardexpert.co.uk, gambling.com and flightcomparison.com.
The firm has a £6m pot to invest and buy new companies, with several deals in the pipeline, Vincent said. The money will be used to continue repositioning Media Corp as a company with two main divisions covering internet publishing and online ad sales.