[nitrogen]

It looks like HDMI uses separate pins from the video signal for Ethernet and Audio Return Channel. I originally thought it was using a shared packetized bus for HEC, but it's actually kind of clever -- differential mode signal on those two pins is HEC, common mode signal is ARC.

HEAC utilizes two lines from the connector: the previously unused Reserved pin (called HEAC+) and the Hot Plug Detect pin (called HEAC−).

- https://en.wikipedia.org/wiki/HDMI#HDMI_Ethernet_and_Audio_R...

So if you don't need ARC, it should be possible to make a simple filter that blocks both HEC and ARC. Older HDMI cables that might not connect the Reserved pin might also block HEC+ARC. And it also seems like you can get ARC-only by disconnecting the Reserved pin.

I'd guess HEC is most commonly going to be used in situations where you'd also want ARC -- to provide network access from an A/V receiver to a smart TV, and then get the audio back into the receiver.