This is interesting - I had previously assumed that a TV’s internal speaker volume could be controlled via HDMI CEC, but that’s clearly not the typical use case. The original/typical HDMI CEC use case is to adjust the volume on a specific external device (an AV receiver or soundbar) using the TV’s remote.
It would complicate matters when configuring a home theater system if one needed to specify multiple devices that control volume, and most folks simply want the TV’s speakers to be muted when they have a proper AV receiver or a soundbar attached to it (hence a single ARC/eARC-enabled HDMI port on TVs that have several HDMI ports). It would be annoying if all connected devices with speakers including TVs responded to HDMI CEC volume control signals, so most TVs don’t (including my 2020 model LG). Perhaps with more ATV/Roku/Fire devices and their remotes out there, we’ll see TV manufacturers make this a configuration option (although I’m sure they would much rather sell us a soundbar instead). Anyone familiar with a modern TV with this option?
My own setup includes an ATV4K device connected to a (Sony HT-Z9F) soundbar which in turn is connected to the LG TV’s eARC HDMI port. With the ATV’s “Control TVs and Receivers” option set to On and the TV’s audio output set to “HDMI ARC”, the ATV4K automatically chooses “Auto via HDMI (Receiver)”. When I experimentally changed the TV’s audio output to “Internal TV speaker”, the ATV4K immediately and automatically switched Volume Control to “Auto via IR (TV)”. Well done, Apple.
Now that ATV4K devices can have their own (virtually) internal speakers in form of HomePods set as the default audio device, Apple added eARC support to the latest version of the device. Also well done!
@Urquhart1244, I seem to recall that I once contradicted you on your assertion that TV volume is only controlled via IR… Sorry about that!