The video ad is triggered only after you click on the message and it's a small 160x140 video that uses the Google Video player. The ads are very short (around 30 seconds) and they end by displaying a clickable URL to the landing page.
Google uses the same visual elements as for the search results and user are already used to previewing YouTube videos by clicking on the small plus sign bellow the snippets. Unlike the video search results, Google doesn't include thumbnails next to video ads, but this may change in the future. Overall, the video ads from Google's search results aren't annoying, they must be explicitly selected and they offer more details that couldn't be included in the short text ad.