It was time to finally upgrade my RPi with the latest libreelec. I hesitated all this time because of loosing the ability to use hyperion with the internal grabber.
Now i had to buy a HDMI splitter (a usb HDMI grabber i already had lying around). Which makes for now a very cluttered setup because of all these cables
I bought the cheapest splitter i could find on amazon only to find out, that it doesn´t support CEC.
So what does a hacker do when something doesn´t work the way it should? Opening the device of course!
The chip is a macrosilicon ms9332 which indeed does not support CEC but the pins necessary for CEC (13,17) a not connected at the board.
So the solution was to connect these pins from the HDMI input to output 1.
EDIT: Ups...wrong category...this should better be in Tutorials. Sorry