Online video ad spending will continue its rapid trajectory this year, and into the next two years, with high double-digit rises as marketers move money from traditional video into digital video, predicted ZenithOptimedia, in its latest advertising market forecast. Overall ad spending in the U.S. in 2012 should rise 4.3% this year, an upward revision from ZenithOptimedia's 3.6% prediction this summer.

Online video viewers are going deeper. A quick analysis of Nielsen's online video statistics at various points in the last year reveals that while the number of online video viewers in the United States has remained steady, they're watching more -- a lot more streams, in some cases -- at the top destinations, and that's where the growth in the business is coming from.