Of course, you could try to open up or bypass the DRM module (e.g., via the GPU driver during hardware accelerated decoding), but that won't work with a TPM module and signed kernel space.
If you look at the security technologies introduced into consumer decides over the last decades, it all serves the dual purpose of securing your hardware from ... you.
Nope. Thanks to HDCP the data never hits the kernel or the host memory unencrypted. It doesn't even require TPMs or signed kernels.
Also, if the DRM module supports hardware decoding, the GPU will need to see a decrypted stream. The GPU memory is in principle accessible to the driver. So if you can manipulate the driver, or setup another kernel module, you might be able to grab that content.
Apparently they present as a compliant HDMI output to the source device, but they don't require HDCP or similar on the output they're passing it on to.
From there, you're free to do whatever you want with the output.
Manufacturing non-compliant devices could become extremely risky.
the monitor itself is doing the unencrypting. As the other person said, it's specifically to protect the video from ... you.
Alternatively you plug into the output of the decryption module in the monitor before it hits the screen?
I believe you can also in some instances skip the hardware capture card and instead capture the data stream out of the host's RAM.
Inside the monitor, the decryption module and the main SoC controlling the hardware are usually the same physical chip, so grabbing data there will be close to impossible.
Some blu-rays force you to update before you can watch them. Also, the key revocation lists can (I believe) be included in the blu-ray itself to make them work offline, too.