ComScore released their monthly report Monday, concerning trends in the viewing of online video in the United States in January 2012, and some of their findings were somewhat surprising. For instance, video viewership was down from the previous month, overall, while the average length of the videos being watched was up.

181 million users viewed over 40 billion videos online in January, as compared to 182 million users who viewed 43.5 billion videos in December 2011. Meanwhile, the average length of videos viewed online in January, as opposed to December, was 6.1 minutes and 5.8 minutes, respectively.

The average viewer watched 22.6 hours of online video over the course of January.

One aspect of comScore's report was a surprise to no one, mainly that YouTube was the top source of online video. YouTube ranked as #1 with 152 million unique viewers, followed by VEVO with 51.5 million, Yahoo! Sites with 49.2 million, Viacom Digital with 48.1 million and Facebook.com with 45.1 million.

40 billion videos views occurred during January, with Google Sites generating the highest number at 18.6 billion.  Hulu was the next highest, with 877 million and VEVO coming in third, with 717 million.

Interestingly, Hulu delivering the highest number of video ad impressions at 1.4 billion. Our opinion on this stat is that people go to Hulu to watch full-length television episodes, and more likely to go to YouTube for video clips. Adap.tv ranked second in ad impressions, with 652 million ad views, followed by BrightRoll Video Network with 598 million, Tremor Video with 580 million and Specific Media with 398 million.

The average online video ad was .4 minutes long, according to comScore. Video ads accounted for 12.2 percent of all videos viewed and 0.9 percent of all minutes spent viewing video online.

Part of the reason why January's slight decline in online video viewership was a surprise had to do with another comScore report, released a few weeks ago. This report predicted that 2012 would be the biggest year ever for online video.

This previous report showed that more than 100 million Americans watched video online on an average day closing out 2011, which is a 43% increase from the year previous. In December 2011, 43.5 billion videos were watched online, up 44% from 30.1 billion in December 2010.