As more Americans get used to watching video on their computers, websites offering free movies, TV and clips are enjoying a 13 percent increase in web traffic from the previous month.

U.S. Internet users watched a record 14.3 billion online videos in December 2008, according to a study by the comScore Video Metrix service.

YouTube itself contributed 41 percent of the online viewing growth, attracting around 5.9 billion views in December.

Its closest competitor, Fox Interactive Media, lagged behind with only around 445 million views, contributing 3.1 percent to the online growth, followed by Yahoo with 330 million views (2.3 percent) and Viacom Digital had 291 million views (2 percent).

Hulu continued its growth trajectory, climbing 6 percent from November to 241 million videos viewed. The average time viewers spent on Hulu was 10.1 minutes, higher than the overall average of 3.2 minutes.