The online metrics company comScore has just published its U.S. online video rankings for December 2011. While the holiday season was great for Google’s YouTube, it looks like Facebook’s popularity might be waning.

YouTube remains in first place with 157 million unique visitors during December. Those visitors spent an average of 471.9 minutes on the site and watched 21 billion videos. The music-focused network VEVO came in second with just over 53 million unique visitors.

Facebook, which came in third place in November, has fallen into fifth place, just behind Yahoo’s properties and Viacom Digital. The social network dropped from 50 million unique visitors to a little over 42 million in just a month.

The number of videos watched also dropped significantly from 270 million in November to 240 million in December. On the bright side, the length of the average number of minutes watched on the social network went up from 19.1 to 23.9 minutes.

It’s possible that the drop is due, in part, to the holiday season. However, Facebook had 60 million uniques in October and has fallen since then. Comments on TechCrunch’s article suggest that Facebook’s redesign has a part to play in its decline.

That theory might not be too far-fetched considering that users’ News Feeds and Tickers are becoming cluttered with various actions across the site. It will be interesting to see if traffic picks up, or if it’ll continue once Facebook’s new Open Graph Actions are launched.

While this isn’t an immediate threat to brands that share videos on the social network, it’s a good reminder to establish and maintain a YouTube presence. Videos uploaded there can easily be shared among other social networks.

[Via: TechCrunch, Image credit: Mark Matson]