Online video viewing in the U.S. broke new records in the month of December, according to the latest research by comScore's Video Metrix service.

The research firm's stats indicate U.S. Internet users watched a staggering 10 billion videos in the month of December, with Google's YouTube service leading the charge as the most viewed destination site for videos.

"YouTube represents almost a third of all videos viewed on the Web for December," Andrew Lipsman, senior analyst at comScore, told InternetNews.com. "And YouTube's total keeps going up. It's 12 percent higher than November."

Google's combined video sites accounted for 43 percent of unique video viewers in December. The next five, Fox Interactive Media (23), Yahoo (20.8), Time Warner (14.8), Viacom Digital (13.3) and Microsoft (10.9) were the only other Web properties to reach double digits in percentage share.

As in search, a combination of Microsoft and Yahoo's share would represent more formidable competition to Google but still trail the market leader. Microsoft is trying to acquire Yahoo.

Lipsman said it was hard to draw any correlation between the Hollywood writer's strike and increased online video viewing. "I suspect more TV viewers are simply switching from their favorite shows to sports and news programs," he said. "But we have seen in the past few months a strong increase in online video viewing, which suggests there is a need for fresh content that sites like YouTube fulfills."

If the writers strike is a factor, Lipsman said its resolution won't necessarily mean a downturn in online video. He said when consumers learn new habits there's often a "step effect" that leads to longer term adoption.

For example, for years there's been an uptick in consumers trying online shopping at Christmas time. "But after the holidays we don't see a big drop off, the numbers stay at that level and then go up again a year later," said Lipsman. He thinks online video could also hang onto its new viewers and continue growing as new ones step in.

Google/YouTube is also involved in lawsuits by media companies that say the site is a haven for illegally posted copyrighted material. Google has said it removes any videos it finds shouldn't be posted and is developing more sophisticated video ID technology to filter out and more quickly identify such material.

Overall, online viewers watched an average of 3.4 hours of video in December, a 34 percent gain since the beginning of 2007. There were 77.6 million viewers on YouTube, who averaged a little more than a video per day for the month (41.6 videos each). Next was Fox's MySpace.com with 40.5 million viewers and 8.2 videos each for the month.

YouTube viewers were just about in synch with overall average viewing time, though its sheer volume also had great influence on the final numbers. comScore said the average time U.S. consumers spent watching a video on YouTube was 2.6 minutes, while the average for videos on all sites was 2.8 minutes.