• by Mark Walsh  @markfwal, June 4, 2010

When it comes to in-stream video ads, 15- or 30-second spots are the standard. But what's the optimum length for a branded video or in-banner video ad? Thirty seconds to 1:30, according to new data from video ad and analytics firm TubeMogul.

The completion rate for stand-alone video ads of that length is at 32.2%, compared to 23.4% for ads longer than 1:30, and 17% for ads under 30 seconds. The assumption would be that the shortest ads would have the highest completion rates. "But what people seem to be saying is: 'we don't like 15-second TV-style spots or longer branded content, but rather short, interesting viral clips,'" said David Burch, communications director at TubeMogul.

The findings were based on a sample of 100 top video ad campaigns, spanning 19.7 million views primarily on YouTube from unpaid promotional videos and paid placements (click-to-play 300 x 250 units), and included brands such as Hyundai and Microsoft.

While the one-third completion rate for mid-length video ads may not sound so high in itself, it compares fairly well with non-ad content. Clips of network TV shows, for instance, have a finish rate of 37.8% -- and music videos, 28.5%, according to TubeMogul.

In-stream ads remain the dominant video ad format, however. Despite experimenting with other types of video ads, 35% of publishers said in-stream video ads produced the most revenue for their media business compared to other ad formats, according to first-quarter research released jointly last month by TubeMogul and Brightcove. Because viewers have to watch pre-rolls or mid-rolls to watch or continue watching a clip or full-length show, completion rates tend to be higher.

Chris Allen, vice president and director of video innovation at Starcom, said completion rates for 15-second and 30-second spots both tend to run 75% to 80%, whether in long- or short-form content. The Interactive Advertising Bureau has said video overall was the fastest-growing segment of U.S. online advertising last year, with revenue increasing 39% to $1 billion.