That's kind of how it used to work before the forced use of MPRIS.
Without this change, only the latest used media player will receive the
signal, which mean that, when I open a video on Firefox, the play-pause
signal will be sent to Firefox and will therefore pause the video
instead of the music I was listening to with Rythmbox.
Since version 3.4.5, Rhythmbox dropped the mmkeys plugin, stating that
it is "no longer useful" and it "has been obsoleted by MPRIS". This
change broke the media keys support on i3.
Since the regression is on purpose, there might not be no way to get
this mmkeys plugin back in Rhythmbox. The workaround is therefore to use
MPRIS. I chose playerctl since it is the most straightforward to me. A
few i3 key bindings later, media keys were back in control of Rhythmbox!
https://gitlab.gnome.org/GNOME/rhythmbox/-/blob/v3.4.5/NEWS0cdeb7cb7ahttps://wiki.archlinux.org/title/MPRIShttps://i3wm.org/docs/userguide.html#keybindings
The default keys used to change focus were close to the ones used in
vim, but not the same, therefore being confusing. Because of that
they were not used and can be safely removed.
Furthermore, one of them is now mapped to the lock screen shortcut.
