But it's not cannibalising viewing of traditional TV.
Active mobile video users grew by 57% to 17.6 million people between Q4 2008 and Q4 2009, according to new research published by The Nielsen Company.
It suggests that this increase is directly linked to strong sales of smartphones during 2009.
The claim was contained in Nielsen's Three Screen Report, whose big finding is that new online and mobile ways to watch shows aren't cannibalising traditional TV viewing.
In fact, in December 2009, 59% of Americans reported multi-tasking - using the internet at the same time as watching TV.
"The initial fear was that Internet and mobile video and entertainment would slowly cannibalize traditional TV viewing, but the steady trend of increased TV viewership alongside expanded simultaneous usage argues something quite different," says Nielsen's Matt O'Grady.
Article continues belowAdvertisement
The report claims that the average American now watches almost 35 hours of TV, two hours of timeshifted TV, 22 minutes of online video and four minutes of mobile video every week.
"We seem to have an almost insatiable appetite for media, with online and mobile programming only adding to it," says O'Grady.
