YouTube's server-side ad injection is a method where ads are directly added into the video stream. This means the ad becomes part of the video being streamed to your device, making it indistinguishable from the video content itself. This approach prevents ad blockers from intercepting and blocking the ads.

Server-side ad injection affects SponsorBlock by offsetting all timestamps due to the ad times. SponsorBlock is a crowdsourced extension designed to skip sponsored segments, but with the ads now being part of the video stream, the timestamps for skipping are no longer accurate. To mitigate this, the developer has set up the server to detect and reject submissions from browsers where this is happening, preventing incorrect data from filling the database.

YouTube is implementing server-side ad injection as part of its ongoing efforts to counter ad blockers. By making ads indistinguishable from the video content, YouTube aims to ensure that ads are shown to users despite the use of ad-blocking tools. This is part of a broader strategy that has included targeting browser extensions and third-party clients.

Server-side ad injection poses significant challenges for ad blockers because it integrates ads directly into the video stream, making them indistinguishable from the video content. This method prevents ad blockers from identifying and intercepting the ads, rendering traditional ad-blocking techniques ineffective. As a result, users may need to seek alternative solutions, such as subscribing to YouTube Premium, to avoid ads.