Wait first dose youtube ads now?
https://drive.google.com/file/d/0B5_hE-brjafocEJGMUR2SXIwV2s/view?usp=drivesdk
https://drive.google.com/file/d/0B5_hE-brjafoNmR2enVueTVxMjQ/view?usp=drivesdk
That might be a part of https://www.youtube.com/watch?v=(https://support.google.com/youtube/answer/6147712?hl=en), and you’re seeing them based on what videos you’ve watched previously.
As Hallry said it does take into account what you watched in the past and posterizes (pretty sure this isn’t a word) your videos with ads associated with them. At least they are awesome FIRST ads and not clickbait ads for nonsensical info. 