• by Mark Walsh  @markfwal, March 30, 2011

The mobile video audience grew about 40% in both the third and fourth quarters of 2010, ending the year at 24.7 million, according to Nielsen. That total was up about 10% on a quarterly basis from 22.9 million.

Mobile viewers watched an average of four hours and 20 minutes of video per month in the fourth quarter -- a 20% increase from the year-earlier period.

That was a bit less than the 33% year-over-year growth in time spent in the prior quarter, and the 4:20 average monthly total was flat from the third to the fourth quarter.

More recently, the turmoil in North Africa and the Middle East and the catastrophe in Japan have led to a spike in video viewing. Mobile TV service mobiTV said the average hourly minutes on its subscription-based offering jumped 500% on March 11, as people checked live updates on ABC, CBS, CNBC and other news outlets about the tsunami hitting the Japan coast.

In terms of audience demographics, Nielsen found those ages 25 to 34 accounted for the largest proportion of mobile video watchers in the fourth quarter, at nearly one-third. People ages 35 to 49 made up 27% of the audience and 18- to-24-year-olds made up 17%.

Teens again made up only 11% of mobile video viewers, but were the most avid audience segment, watching an average of 7:13 a month. Still, that was down from 8:40 in the third quarter. The college-age crowd, however, increased from an average of 5:25 to 6:30 to help offset the decrease in viewing time by teens.

The overall mobile video audience remains small at less than 10% of the roughly 230 million U.S. mobile users ages 13 and over. But with a growing number of people buying media-centric smartphones, mobile viewership is expected to expand. Nearly a third (31%) of U.S. cell phone users owned a smartphone at the end of 2010, compared to 23% a year ago.