I noticed there is volup and voldown in
cec-client commands. But how do I know the current level to make the Raspberry Pi adjust it? Or is it possible to set a percentage?
I used scan, but it didn't notice that information.
cec-client allows you to pipe cec frames, such as
echo "tx 20:71" | cec-client RPI -s -d 1. http://www.cec-o-matic.com/ has a list of supported features and frame composer/decomposer. https://blog.gordonturner.com/2016/12/14/using-cec-client-on-a-raspberry-pi/ has more information on how to use these with cec-client.