More than four in five users find in-stream ads on web video clips “annoying”, according to a study by Forrester Research.

Covered by AdWeek, the report showed online video users find less-intrusive forms of advertising more acceptable, such as placements alongside clips.

Of the web video viewers polled, over 80% found ads inserted into content annoying, while 75% said they ignored them. Half were happy with placements, while only 19% were irked by text links.

Those figures will be interesting reading for advertisers looking to target audiences on sites such as YouTube, and as online communities test how best to use their video content to make money.

As Forrester said, the unpopularity of video ads could also be a problem, as they are typically the best way to convey messages.

Brian Haven, an analyst at Forrester, added: “Marketers need to think differently about how they’re communicating with their customers viewing online video.”

Meanwhile, another study says over $2bn of US ad spend will go on social networking sites by 2010.