It’s not that YouTube is alone in these efforts many digital publishers make similar attempts to stymie ad blockers. As noted in a blog post by the ad- and tracker-blocking company Ghostery, YouTube employs a wide variety of techniques to circumvent ad blockers, such as embedding an ad in the video itself (so the ad blocker can’t distinguish between the two), or serving ads from the same domain as the video, fooling filters that have been set up to block ads served from third-party domains.
