I use multiple media players, Play Music, Musicolet for local media, and a podcast player. I set it up so no matter which one I'm listening to, I can control it via shortcuts.
I then used a Webscreen bubble to control my media, so I can control it anywhere.
To get it to work, you will need to change all the media control actions to work with your own players (alas, each player uses a unique intent to play/pause/skip, so this step is necessary).
UPDATE: The latest version gets around this requirement with AutoShare! Just get all the Media Intents available from inside the app, put your players in the AutoNotification Intercept, and you're all set!
Control any music player with FAB 1.2
Floating button to control your current music player.
- AutoShare required, no need to edit Player buttons Sep 3, 2018
- Fixed bugs, changed notification intercept May 29, 2018