I don't understand why the OS disables the audio controls of HDMI outputs. If I press the volume down button, I want the volume to go down. Instead, I get a "I can't let you do that" warning!
This is particularly bad if I have my headphones connected to the display (I have both my desktop and laptop connected to the same display, keyboard and mouse, being able to share the same headphones would be pretty convenient).
If you think of all the devices that output via HDMI, Windows PCs are the outlier (afaik, not sure how Linux handles it) in allowing separate volume controls beyond those on the output device.
Satellite set top boxes, media streaming devices (e.g. Apple TV - I realise NVidia Shield and some Chromecast apps do have some software volume control), games consoles, and Blu-Ray players will all output a fixed audio signal, expecting the TV/AV amplifier to handle volume.
The devices are supposed to coordinate on which device will output audio (TV, sound system, etc.), and they are supposed to send control signals (volume up, volume down, and mute button presses) in a channel over the HDMI connection so that whatever device is playing audio can adjust its volume.
Of course this assumes all devices involved implement CEC (which is optional) and that the implementations aren't full of bugs. But the point is HDMI does have a solution for this in theory.
CEC is how I can punch the volume control on my Samsung TV remote and the volume on my Denon AV receiver changes. (And it's not the TV remote transmitting IR to the receiver. Within the first 5-10 seconds of powering on, pushing volume up on the TV remote makes the TV try to adjust its own volume even though it's not playing audio. Then it comes to its senses and realizes it should be forwarding that via CEC.)
I think they forgot the "consumer" part of "consumer electronics control".
It really takes away from the appeal of a convenience feature if it requires periodic battles to beat the equipment into submission.
I have experienced the pain of broken CEC with my previous Hisense TV though.
But you’re spot on. Even my techie friends struggle getting it right with audio over Discord
Analog sources could vary in volume because they provided voltage across an analog input. When CD players came out, they had notoriously "hot" outputs, meaning physically higher voltage. Not so with digital connections.
I genuinely think that statement might be false in more cases than it's true. Certainly in devices I've used personally, the majority have allowed you to control the output volume directly.
Maybe that's a regional thing, but I think that all set top boxes (and DTV decoders) that I used had it's own remote with adjustable volume.
You can install https://github.com/MonitorControl/MonitorControl with uses Display Data Channel (DDC) to let you adjust volume and brightness on external monitors. It works for my monitor at least.