As you can see, this is possible in icon Volume > Applications for mpv.
However, it does not appear as such in the taskbar.
Elisa Player display a small icon of volume when a file being played, but doesn’t display a paused icon, or playing/paused on tray Volume > Applications.
I think there is a need for adjustment or new control icons feature for multimedia actions on taskbar.
Audio player for example Elisa, it display a little volume indicator, but not for (mpv video player), haven’t checked with other video player like VLC since i only use mpv for videos.
However, I am asking for indicator “playing / paused” icon to be made over player, not a simply volume icon. Just as it is on Tray > Volume > Applications.
I made a simple play/pause desktop application which uses playerctl. I tried it with smplayer, vlc, audacious, brave browser. Works fine BUT it does get tricky when there are two instances of media open. I mean, let’s say you have a paused media file in, say, vlc and you’re watching a youtube video. Then the simple playerctl play-pause will get confused on what to do. Guess you’d need some kind of script which checks the active instance first. I believe I came across such a script somewhere. Now, as far as mpv goes, you’d probably need the mpris plugin anyway if you just want a simple play/pause function on your panel.
That being said, a play/pause function instead of mute on the task icon kinda makes more sense.
Elisa doesn’t display that tray icon you get from video players? That’s probably a bug.
Your request makes sense, as why would one “mute” a music player instead of pausing it? But I’m not sure if it’s worth special-casing for music players, as the badge is “mute” for all other types of apps. Your best bet is the media player tray icon.