YOUTUBE LOOKS TO BE TESTING SERVER-SIDE AD INJECTION TO COUNTER AD BLOCKERS

Summary from the TLDR newsletter

YouTube is currently experimenting with server-side ad injection. It is making ads part of the video being streamed instead of delivering them separately, resulting in them being indistinguishable from videos. The implementation breaks extensions like SponsorBlock, which depend on timestamps to mark video sections. Server-side ad injection is still in testing and not yet widely rolled out.