If you have HDMI, the EDID comes through on the DDC which is just I2C. You can read it with a BusPirate or any decent LA: https://www.extron.com/company/article.aspx?id=uedid

HDCP also happens over this interface, so it’s trivial to snoop on the key exchange: https://github.com/ApertureLabsLtd/hdmi-sniff/blob/master/RE...

CEC (control devices via HDMI) happens on a separate channel using a proto also similar to I2C: http://www.quantumdata.com/pdf/CEC_White_Paper.pdf

There are a few good ~cheap CEC adapters for HDMI out there. I’ve used the PulseEight one since they have decent library support plus a CLI. You can also use the HDMI port on a Raspberry Pi to play with CEC: https://github.com/Pulse-Eight/libcec/blob/master/docs/READM...