While YouTube and its parent Google (NSDQ: GOOG) have been promoting ad overlays as the best format for supporting online video, the video site has been slowly employing post-roll the past few weeks, NewTeeVee has confirmed. YouTube began considering using post-rolls to augment its pre-roll and overlay ads this summer. But the decision to go ahead with the format represents something of a reversal for the site. In July, Google CEO Eric Schmidt said the company had evidence that embedded video ads were much more effective than both pre- and post-roll. Users probably won’t feel too put out by the introduction of post-roll, which can obviously be avoided since the video a user chose has already concluded. But it does suggest that YouTube is still struggling with its ad strategy. And as NewTeeVee pointed out, post-roll only runs on a sliver of the roughly 4 percent YouTube videos uploaded by official partners taking part in the site’s revenue-share deal.