Those are two of the main findings of a new study conducted by InsightExpress on behalf of Advertising.com regarding online video viewing habits. According to the study of 500 adults ages 18 and older, nearly half of streaming video users were likely to watch news clips or music videos (48.6% and 47.4%, respectively). About a third (32.6%) of the respondents were likely to watch streaming music videos.

Notably, only two of 10 online video users said that they were likely to stream user-generated content. This means a lot of user-generated content may go unwatched, since such content is expected to comprise more than half of all online video by 2010, according to Screen Digest. (Full article yesterday.)

According to the Advertising.com study, the vast majority (87.9%) of video streams are viewed at home, while 8.5% are viewed at work and 3.6% at school.

The type of content viewed by study respondents depended on age. Viewers ages 35 and older were 24% more likely to watch news clips than the overall group. Similarly, respondents ages 18 to 34 were 38% more likely to watch streamed music videos than the group as a whole.

Knowing who is viewing online video and what they are watching will become increasingly important during the next few years, as roughly half the US population (157 million people) will view online video monthly by 2010, up from 107.7 million in 2006.

David Hallerman, author of eMarketer's recent Internet Video Audience report, notes that "while Internet video, and the audience for it, is clearly at a primitive stage, it is equally clear that with 107.7 million viewers this year and more than 150 million by early 2010, a huge audience will be available — and it is up to advertisers and content providers to seize the opportunity by creating ever more effective ways to get in touch."

For more on who watches online video, and what they watch, see eMarketer's recent Internet Video Audience report.