Pre-roll video ads beat out transitionals - between-page units - in generating brand awareness and message association, but transitional units produce greater intent to purchase, according to research by rich media tech firm Viewpoint with assistance from Dynamic Logic, report ClickZ and MediaPost. Video ads that ran embedded within banners were the least effective among the three formats.

Pre-roll increased brand awareness 96 percent and message association 272 percent, compared with a control group, according to the study. Transitional units are better at increasing brand favorability and purchase intent, generating a 23 percent increase in each, whereas pre-roll showed no increase in either. Viewers also reported relatively less irritation with online ads than television ads.

For the study, Viewpoint streamed 40 million 30-second online video impressions for four separate campaigns, over eight weeks, across various sites, including About.com, CBS News, CBS SportsLine, America Online, ESPN, iVillage, and Weather.com. Dynamic Logic then surveyed approximately 3,800 online viewers who were exposed to the ads.