• by Mark Walsh  @markfwal, June 10, 2013

The U.S. mobile video audience in the first quarter reached 45.3 million, up from 36 million a year ago. That 25% gain made the mobile phone the fastest-growing platform by viewership in the last year, while audiences on traditional TV and desktop Web actually slipped, per Nielsen’s latest cross-platform report.

The number of TV viewers fell slightly to 282.9 million from 283.3 million, while the PC-based video audience dropped from 162.5 million to 155.2 million. In terms of average time spent per user, however, TV and the Internet still far outpaced mobile. People spent five hours and 29 minutes a month watching video on a mobile phone, up from 5:01 a year ago.

That compares to 28:28 on the desktop Web (down from 30:05), and 157:32 on TV, up from 155:46. Not surprisingly, young people tend to be the heaviest mobile video viewers, with teens (12-17) watch the most on a monthly basis at 7:51. People 18-24 watched the most weekly, at 27 minutes, with teens logging an average of 23 minutes.

Among ethnic groups, Hispanics made up 20% of mobile video watchers, followed by African-Americans (17%) and Asians (8%). African-Americans spent the most time viewing video on phones at 6:21 per month, with Asians at 5:55 and Hispanics a close third, at 5:44.

The Nielsen Cross-Platform report also took a more in-depth look at media use on smartphones and tablets in the first quarter. “In the spectrum of evolving media, nothing is growing faster than the adoption of portable devices or the consumption of content on these devices,” stated Dounia Turrill, senior vice president, Insights at Nielsen.

Users on both devices spent the vast majority of their time with apps versus the mobile Web. Smartphone owners devoted 87% of their time to apps, equating to almost 26 hours for men and 28 hours for women, each month.

Similarly, iPad users spent 76% of their time with apps, or 12:24 for men and 15:05 for women, each month. When it came to streaming video, iPad app users spent 1:48 per month doing so versus 1:15 for smartphone app users. Social networking activity, however, was far heavier via smartphone apps, at 9:06 compared to 3:41 on iPad apps.