The number of internet users in the U.S that watch or download online videos has grown significantly over the last four years, according to new research, but the types of videos that are most popular may be a surprise to many.
Some 78 percent of online adults now watch online videos, compared to 69 percent in 2009, according to a telephone survey conducted by the Pew Research Center. Over the same period, the percentage of American adult internet users who shared or posted videos online doubled from 14 percent 31 percent.
But when it came to the most popular genres of video, comedy and educational videos topped the list, with 57 percent of the 1,000 people questioned saying they watched funny videos and 50 percent saying they watched educational videos.
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Meanwhile - languishing at the bottom of the list - was adult videos, with only 12 percent of internet users saying they viewed porn online. A quarter of male online video watchers questioned said they watched this genre, in contrast to just 8 percent of the women.
"This may reflect a reluctance to report the behavior among some adults," the report said - a view backed up by Richard Broughton, head of broadband media at research firm IHS Screen Digest.
"If the methodology is survey-based, I suspect no-one is likely to admit to watching adult films – other (non-survey-based) viewing data suggests otherwise," he told CNBC.
"However, it is certainly true that comedy series do well online, and that some of the most popular YouTube channels are comedy-based. Often, such shows are targeted at the demographics which are more likely to be connected and willing to view content online – comedy also prompts discussion in a way that many other genres don't, which helps to fuel its success."
Earlier this year, porn website Paint Bottle published non-survey-based research on adult video viewership, bringing together statistics from a variety of sources including Google searches.
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It suggested that adult sites got more visitors each month than Netflix, Amazon and Twitter combined, and claimed that 30 percent of all data transferred across the internet was porn.
YouPorn, one of the larger adult video sites, streamed six times the bandwidth as general video streaming site Hulu, according to Paint Bottle's research, implying that more people were using the porn site than its mainstream rival.
'Surge in viewership'
What is clear from Pew's survey, however, is that online video is huge - and growing.
The increasing popularity of social networking sites and the proliferation of smartphones have helped spur this growth, according to both Broughton and Pew Research.
A growth in the take-up of tablets and smart TVs, faster broadband connections and a surge in rights availability were other key drivers, Broughton said, with more content owners making their shows available online, which in turn is fueling viewership.
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Mobile research firm Juniper Research recently predicted that by 2017, 2 billion mobile and tablet users would watch TV and video on their devices, while revenues from streaming and download services on mobile and tablet devices would reach $9.5 billion - up from $4.5 billion this year.
"This surge in viewership has significantly altered the business models of market leaders here – subscription services are becoming the de facto means by which to monetize content across TV, laptop, mobile and tablet. Netflix, Hulu and Amazon are leading this change in terms of online viewing," Sian Rowlands, a research analyst at Juniper, told CNBC.
"While Apple's App Store and Google Play Movies offer TV and movies to stream for a one-off cost, we wouldn't be surprised if they are considering launching a subscription service in the near future."
—By CNBC.com's Matt Clinch; Follow him on Twitter @mattclinch81