Custom firmware and CEC?

[Trev]

So presumably the TV's HDMI port(s) circuitry must be powered when the TV is on standby?

 

[xyz321]

Only the CEC line needs to be powered, presumably the rest of the HDMI circuitry will be shutdown to save power.

 

[Black Hole]

It wouldn’t need to be fully active anyway - just a low-power circuit to detect any activity and wake up the next stage of processing. That’s typical of a micro-controller circuit (just sits in a low-power state waiting for an event to trigger a burst of processing).