I also recommend an insightful talk by the author of the article, delivered at a Chaos Computer Club (CCC) event (GPN, Gulaschprogrammiernacht) on this topic. Unfortunately, it's only available in German, but it's definitely worth watching:
https://media.ccc.de/v/gpn22-382-kein-kinoerlebnis-ohne-korr...
„No cinema experience without correct certificate management... A look behind the scenes of a cinema with a digital projector system, how distributors deliver films to cinemas with end-to-end encryption, and how films are protected from piracy. In addition to an overview of projector technology, the presentation will demonstrate the file format and manual decryption of film data.“
Edit: I just realized that the author of the article also delivered the recorded talk, adapted my comment.