Not that I would ever pirate a movie because I'm a good boy, but I remember the Cinavia DRM that affected Blu-ray players thirteen years ago.

I'm not 100% sure how it worked, but I guess it could do a similar kind of steganography-style thing to the audio track, where they would embed keys silently and the blu-ray player would check against that.

I'm not sure if anyone actually ever managed to defeat it, I think they just stopped implementing it in streaming boxes.