This has been discussed before here. Since then the HDCP master key has been leaked. Is it still nearly impossible to read HDMI input to opencv?
An example device with HDMI input is the Geniatech ATV1610. This looks a lot like the device that skipr uses.
Edit: How about non-hdcp sources? Anyone?
It is not possible because the source device will not send a valid signal to the sink, unless the sink device correctly negotiates a connection with the source. This requires both a valid KSV (40-bit Key Selection Vector) (one that has not been revoked by DCP LLC) as well as valid device keys that correspond to the KSV.
Given that this HDCP handshake is typically done by the same hardware that subsequently decrypts the stream, you find yourself in an all-or-nothing situation. You either have a valid KSV and corresponding sink keys, in which case you can do the handshake AND the decryption. Or you don't, in which case you can not negotiate the link handshake and the source will not send you any data, encrypted or otherwise.