add sound.volumeStep config option

[dermetfan]

Motivation for this change

Issue #17068

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • OS X
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

---

allows user to configure the amount by which volume is increased/decreased by sound.enableMediaKeys

[mention-bot]

@dermetfan, thanks for your PR! By analyzing the history of the files in this pull request, we identified @oxij, @edolstra and @nbp to be potential reviewers.

[edolstra]

I had not noticed the addition of sound.enableMediaKeys (57ab189) but IMHO that sort of thing belongs in the desktop environment, not in the global NixOS configuration. It's not even clear how this interacts with e.g. PulseAudio, multiple sound devices, per-application volume settings etc. So let's not add to it.

[dermetfan]

@edolstra Fair point. sound.enableMediaKeys does not work if PulseAudio is enabled, at least not without hardware.pulseaudio.systemWide = true or other extra work, because amixer is run as root and cannot connect to the user's PulseAudio daemon. That took me a while to figure out when I worked on this change, so even though it's disappointing, I understand your opinion.

[oxij]

Eelco Dolstra notifications@github.com writes:

... IMHO that sort of thing belong in the desktop environment, not in
the global NixOS configuration.

I disagree. IMHO media keys should work from bare ttys (because they
can, also what about all the headless "music box" PCs (I happen to have
one)?).

It's not even clear how this interacts with e.g.PulseAudio, multiple sound devices, per-application volume settings etc. So let's not add to it.

I agree, however, that the name is misleading in that context. I should
have named it sound.alsa.enableMediaKeys and implemented
sound.alsa.config (which would put stuff into /etc/asound.conf).

PulseAudio

That code is for alsa, as described above.

multiple sound devices

It does the right thing by controlling the Master volume of the default
sound device. People with multiple audio cards should configure their
alsa.confs anyway.

per-application volume settings

Not supported in alsa, AFAIK.

[dermetfan]

How about this example configuration.nix then? For backwards compatibility, let's make sound.enableMediaKeys an alias to sound.alsa.mediaKeys.enable.

sound.alsa.mediaKeys = {
  enable = true;
  volumeStep = "1";
};

Also, I would note the incompatibility between PulseAudio and sound.alsa.mediaKeys.enable in the documentation of hardware.pulseaudio.enable so other's don't run into the problem I described in #20020 (comment).

[oxij]

Sounds like a plan.