Sorry to resurrect an old post, but I had a question about your physical setup.
My goal would be to plug my Roku Ultra Into my Denon AVR, into an HDMI splitter with CEC out both sides:
I found this one: Splitter TESmart Support Compatible Blu Ray
I want to run the onside to my TV, the other to the USB video grabber plugged into the raspberrypi which would have nodemcu or arduino for my led controller.
This is where I get confused, does CEC pass through the USB Video Grabber into the RaspberryPi?
No, as mentionned in the first post, you need to plug an HDMI cable from the TV to the Pi.