Modifique ~/.config/openbox/lubuntu-rc.xml (pode ser copiado de /etc/xdg/openbox/rc.xml )
Dentro do elemento <keyboard> adicione o seguinte para suportar o Clementine (ou equivalente para suportar outros players de música):
<keybind key="XF86AudioPlay">
<action name="Execute">
<command>clementine --play-pause</command>
</action>
</keybind>
<keybind key="XF86AudioStop">
<action name="Execute">
<command>clementine --stop</command>
</action>
</keybind>
<keybind key="XF86AudioNext">
<action name="Execute">
<command>clementine --next</command>
</action>
</keybind>
<keybind key="XF86AudioPrev">
<action name="Execute">
<command>clementine --previous</command>
</action>
</keybind>
e execute openbox --reconfigure para recarregar os arquivos de configuração.