Dear Maintainer,
TL;DR: it seems that lxhotkey-gtk (or lxhotkey-plugin-openbox, I don't know who is reponsible for this) detects/writes to the file "AudioLowerVolume"/AudioRaiseVolume"/"AudioMute" instead of "XF86AudioLowerVolume"/"XF86AudioRaiseVolume"/"XF86AudioMute".
Step by step:
I run:
$ xev
And press "VolumeDown" in my keyboard. "xev" says:
-------------
KeyRelease event, serial 48, synthetic NO, window 0x9000001,
root 0x211, subw 0x0, time 151825, (1464,409), root:(1466,432),
state 0x0, keycode 122 (keysym 0x1008ff11, XF86AudioLowerVolume), same_screen YES,
XLookupString gives 0 bytes:
XFilterEvent returns: False
-------------
The "keycode" is XF86AudioLowerVolume. For Volume Up I get XF86AudioRaiseVolume and for the mute button I have XF86AudioMute.
Note that I have a Lenovo and I do Fn+F1 (mute), Fn+F2 (Down), Fn+F3 (Up) with the Fn key enabled. I don't think that the model or combination really matters as long as "xev" is reporting the XF86AudioLowerVolume, XF86AudioRaiseVolume and XF86AudioMute.
On the other hand, in lxhotkey, I try to add a new Action or Program. In the "Hotkey 1" I press "VolumeDown" in my it shows "AudioLowerVolume". I finish my configuration, Save+Apply, etc. and it never works.
If I edit the file ~/.config/openbox/lxde-rc.xml I can see that lxhotkey did:
-------------
<keybind key='VolumeDown'>
<action name='Execute'>
<command>/home/carles/bin/volume-down.sh</command>
</action>
</keybind>
-------------
If I change the "key" in the lxde-rc.xml file from "VolumeDown" to "XF86AudioLowerVolume" and then I do:
$ openbox --restart
it works correctly.
Note that I don't know if this should be dealt better by lxhotkey-gtk, lxhotkey-plugin-openbox or openbox itself should be reading the file differently.
Cheers,
Carles