According to MediaWeek, “Analysts and agency executives envision a new ad system that would use sophisticated targeting techniques to create ad messages users will want to watch.”
Someday tagging will connect video ads to video content. That's viable in the new world of YouTube and Google. Advertisers could buy video ads based on keywords. Then their ads play before or after videos tagged with those same keywords.
Brian Morrissey suggests an AdWords type system which "could choose from a vast pool of video spots for one relevant to the viewer."
For this to work, all publishers showing videos have to take a more active role in tagging as well.