Amazon Prime videos play, but not in HD, citing HDCP error (HD Videos Unavailable, HDCP)

Solution 1:

The protected content would not be streamed over unprotected media. High-Bandwidth Digital Content Protection usually authenticated all devices in chain. So that include application->Display Driver->Graphics Card-> Serializer(on host side) -> deserializer(on display device side) -> Display Device. HDCP usually encrypt data when transferred over cables(HDMI etc). But software that renders data can request underlying device content protection status. So things can go wrong at lots of places.

Problem is most likely with driver of your display adapter/associate serializer. You can try to get latest graphics driver for display adapter and display monitor. Also how are playing video via desktop app or web browser?

Hope this helps

Solution 2:

HDCP is a work in progress. I'm not sure about the status, but comparing the first patch of the RFC to the code of linux-4.13-rc6 I see it didn't land yet.

Stay tuned, I'm pretty sure the day HDCP get the whole stack from kernel through DRM (as in Direct Rendering Manager) to userspace up and running you'll see a big article on Phoronix. It's a slow work because of other things in priority, and because any kind of DRM (as in Digital Rights Management) have always been a subject of hot controversy.