Video is the fastest-growing online advertising format with estimates of about a 40-percent growth rate through 2010. And the marketers that have taken part in its growth are resoundingly satisfied, according to a recent study from video ad network BrightRoll.

More than 50 percent of the agency executives who participated in the study indicated that online video was the most effective form of advertising, and 83 percent said they were getting more value for their video advertising spend in early 2010 than the previous year. A whopping 94 percent revealed plans for spending more on online video ad campaigns this year than in 2009.

Another sign of video advertising’s maturation in 2010 is the more than 60 percent of respondents that said behavioral targeting increased the performance of their campaigns. The targeting capabilities of video ads were cited as the biggest concern among agency execs in 2009. The biggest concern revealed in this year’s study was maintaining credibility with video ads, with executives saying that videos that start automatically were the biggest detractor.