ComScore released its January 2011 US Online Video Rankings earlier this week. The main takeaways are Vevo is hot and the general population’s New Year’s Resolution was to watch slightly less online video.

Vevo snuck into the number two spot behind Google in the category of Total Unique Viewers, with 51,025,000 for the month, a slight increase over its December numbers of 50,594,000. The music video mecca was one of a handful of online destinations (along with Facebook, Viacom, Microsoft, Turner, and Fox) on comScore’s top 10 list to make viewership increases in January, but those gains couldn’t make up for the overall bump in online video’s otherwise solid upward trajectory.

“The total US internet audience engaged in nearly 4.9 billion viewing sessions” in January, down from 5.2 billion in December. After the big online video marketing and advertising boom this past holiday season, video ads are also predictably down, from 5.9 billion in December to 4.3 billion in January.

Hulu maintained its position on top of the Video Ads Viewed chart with more than 1 billion over the course of the month. That’s more than twice the amount of video ads viewed by way of Tremor Media Video network, the next closest competitor.

Two things that did stay constant between December and January are (1) the duration of the average online video at five minutes and (2) the length of the average online video ad at 24 seconds.