What is AdSense for video?

AdSense for video allows publishers with video content to earn revenue using relevant, non-intrusive ad placements from Google's extensive advertiser network. Video content will display both In Video overlay and text overlay ads.

Google has announced a closed beta test of Adsense for Video.
According to the post on Inside Adsense, Adsense for Video consists of “in-stream” advertisements. Publishers define at what point the advertisements will appear for each video.

It’s a change in the right direction for Google. The previously announced
advertising trials for YouTube consisted entirely of text advertising overlays that lead to video-on-video click to play advertisements; a form of advertising that can easily be ignored by the viewer. Whilst many may find in-video style advertising annoying, it at least comes with a guarantee that viewers are going to see the advertisement.

Adsense for Video, as it is currently explained lacks contextual delivery. Allowing publishers to select where a video is played may empower content creators, but it does nothing in terms of automatically optimizing advertising for the viewer.