The remaining share of revenues was made up of the online video services of major sports leagues, video services from traditional online portals, and direct services from other major channel groups and content owners.

The combined dominance of the leading broadcaster supported platforms will drive the total ad-supported model for the distribution of online entertainment programming, news, sports and events in the U.S. to more than $1.45 billion in revenues by 2013.

"With better targeting and increased ad inventory, online TV services could be generating per-viewer revenues comparable to an average TV broadcast viewing in as little as three years," said Arash Amel, Research Director, Digital Media, Screen Digest and author of the report.

However, based on the current online ad strategies implemented, it will account for 2.2 percent of all US TV advertising revenue by 2013, but definitely won’t be generating enough to offset the $2bn we expect total US TV advertising to have declined by during in that period.

The major U.S. broadcasters are evolving into a multi-platform TV distribution networks in an attempt to mirror their traditional channels business online. The multi-platform approach has been and will remain important to the future relevance of broadcasters to younger demographics and retaining prime position in the online TV space.

The key will be to create an online platform model that allows for control of the content while distributing it widely, and meets the audience’s changing demands for TV anytime.

"A successful online entertainment distribution business model is about establishing and maintaining interest in trusted brands and syndicated services that go hand-in-hand with the content, often free at the point of audience consumption, said Amel.

This year will be a challenging one for TV advertising, with spend growing at a lower rate than the economy at only 1.9 percent in Europe and 1.5 percent in the U.S. TV advertising will receive a boost from major events that occur every four years including the Beijing Olympics, the European football championship and the U.S. elections.

The benefits of those events will help avoid a recession for TV ad revenues but the effect will be temporary setting up a fragile advertising environment in 2009. Screen Digest predicts marketing budgets will be cut, especially in the U.S.

"Advertising spending tends to amplify economic cycles – and in some instances it actually anticipates downturns. Although we’re not expecting advertising budgets to be affected this year, thanks to the quadrennial eventswe’ll experience the real impact in 2009, which will be the toughest year for advertising revenues," said Vincent Ltang, Screen Digest Senior Analyst and author of the research.

The growth rate in 2011-2012 will be higher as the economy picks up after 2008/2009, at 5 percent in Europe and 6 percent in the U.S. The majority of this growth will come from online advertising, which is on track to grow on average by 17 percent every year until 2012.

Screen Digest says that by 2012 advertising will be a three tier market with the most being spent online, followed by TV in the middle and traditional media on the bottom. When both search and display are combined, online advertising will see double-digit growth every year to 2012.

"Whilst the overall picture for ad revenues is flat or in decline, two areas will enjoy growth – online will continue to grow at a pace, buoyed up by a strong search advertising market and digital TV channels will be taking a larger proportion of ad budgets by 2012, at the expense of the traditional broadcasters," said Ltang.