Some users might find that initial 50% volume(green level) is too low.
Now the MUTE the VOLUME UP/DOWN should work, for controling your STB. Model specific image should contain that info* how to toggle volume control.
*You have entered a link to a website that the administrator does not allow links to
https://vuplus-community.net/board/threads/volume-up-and-down-button-does-not-work-with-the-remote.42224/#post-275998 https://wiki.vuplus-forum.org/index.php?title=Fernbedienung
PiMyLifeUP
cec-client(with that tool we can also see that vendor is unknown and menu lang. ??? while CEC version is 1.3a)
first thing you will need to do is scan for available devices that are advertising that they have CEC capability
Maybe users would appreciate some kind of easter eggs?
https://www.jblsynthesis.com/on/demandware.static/-/Sites-masterCatalog_Harman/default/dwa02ff977/JBLSynthesis_SDR35_Hero_Web.png https://www.denon.com/-/media/images/denon/avr-x3700h/avr-x3700h-1j_19102020.jpg
Picons are channel logos which are linked to one or more TV channels using a service reference or a simplified version of the channel name.
Anyhow, it should be safe to set vol to max if AV rec. is not present. Some users prefer to use only TV vol control for most time between 12-20%.
Another small issue which might confuse Homer like users...