In-stream video advertising may never be the same after Google gets done with it. Known for populating the web with countless text ads, Google has taken its AdSense program to the video screen, announcing that it will begin selling ads that appear inside videos on any site in its publisher network that serves more than one million video streams per month.

Google, which began testing the pilot program back in May, announced the news on its AdSense blog. The program features InVideo ads -- a format Google developed on YouTube -- and text overlay ads that are contextually targeted based on signals that appear both in the video and on the page.

While Google has limited the number of participants, a who's who of the web video world has already jumped on board. Brightcove, Revver, MyDamnChannel, Tremor Media, Blip.tv and YuMe are among those who have announced that they will participate in the program.

But not all video companies are going along with Google's efforts to monetize the medium, which so far represent a small but growing fraction of total ad dollars spent on the web. In addition to competing with traditional rivals like Microsoft and Yahoo, which recently paid $160 million for Maven Networks, Google also will face competition from the likes of VideoEgg and its new engagement ad model. 

Competition aside, one casualty in the looming battle could be the much-maligned pre-roll ad format. Google's decision to go with in-stream ads and text overlays means a sizeable chunk of the web's video won't have pre-roll.