We may well call this the “Internet advertising” era, if we look at IDC’s latest report on the U.S. market: online advertising is expected to double from $25.5 billion last year to $51.1 billion in 2012, the market research firm predicted on Friday.

Within the next four years, online advertising is expected to become second after direct advertising, from the fifth place it occupies today. According to IDC, the online video advertising will also increase in popularity in the United States.

Furthermore, the revenue from video advertising is expected to grow sevenfold from $500 million now to $3.8 billion within four years. We are now looking at a tendency to shift from cable TV and broadcast television classic advertising to online video advertising, IDC says.

And it’s all because of the consumers, Kirsten Weide, program director for IDC’s digital media and entertainment unit explained: consumers have begun to realize that as opposed to the TV, internet video allows them to watch what they want, when they want, how many times they want.

The forecast for the United States shows a significant growth in online advertising revenue, despite more pessimistic reports that showed stagnation over the past two years in this business.

Earlier this month, an Interactive Advertising Bureau report for the United States unveiled that search advertising accounted for 41 percent of the overall online spending last year, up 1 percent from 2006.

Search advertising appears to keep the secret to online advertising, remaining the dominating form on the market, and led by Google with 70 percent.

As online advertising began developing and will continue to do that in the years to come, Microsoft, Yahoo and others are expected to make bigger efforts to take a piece of Google’s pie.