Substantial growth for online video advertising depends on the audience and the inventory—enough people to watch the ads and enough space to encourage mass marketers to buy the ads.
"With 67% of all Internet users now viewing some form of video advertising—in-stream, in-banner or in-text—at least once a month, the audience has reached critical mass," says David Hallerman, senior analyst at eMarketer and author of the new report, Video Advertising Growth Factors. "At eMarketer, we are estimating that by 2012 four out of five Internet users will view video ads, and that means the ads will be ubiquitous."

eMarketer projects that 129.5 million people will view online video ads this year, and that number will rise to 183.3 million in 2013.
