I had a peek and it looks like it's the youtube lounge API. Basically this is casting with some bonus features. If you are playing on a Screen (a tv or console) then Remotes (usually your phone) can automatically notice it and automatically show what is playing, let you use controls, add stuff to the playlist etc.

This program registers a remote and automatically skips forward when a sponsorblock segment is present.

It blocks sponsored content using SponsorBlock[0], which uses crowdsourced data to detect segments in video's and skips them (basically fast forwards over the content).

[0] https://sponsor.ajay.app/