Online video ad rates keep coming down, but that could be a good thing. BrightRoll, a large video ad network, is reporting that cost-per-thousand (CPM) rates for pre-roll video ads across its network are down on average by 37 percent from a year ago, but total revenues across its network are up 84 percent. Cheaper ads are leading to more spending by advertisers overall.

The chart above shows average CPMs on BrightRoll’s network indexed to 100 at the beginning of 2008. The average CPMs are now in the mid-teens, and seem to be leveling off. They were down 4.5 percent from last quarter.

BrightRoll says online video advertising started a rapid post-recession comeback in the first quarter of 2009 (which is about when video platform company Brightcove starting seeing an uptick in business also).

The third quarter saw an acceleration video advertising. BrightRoll tracked a 46 percent increase in the number of video ad campaigns, compared to the previous quarter, 31 percent more advertisers, and a 64 percent increase in requests for proposals (RFPs). If BrightRoll’s data is indicative of the industry as a whole, online video advertising should remain a bright spot this year.