I think the question is about the media keys. What happens if your phone is playing something on Spotify, and your laptop is playing something on VLC, but also has Spotify open? Does pressing the skip media key make both players skip, or just one of them?
On Windows hold shift then press the media keys to control a second (background) program. Found this out purely by accident in this exact scenario, VLC in foreground and Spotify in background!!!
On Windows VLC will swallow hot keys if it's on top, otherwise they are caught by spotify. If they are both in the background it's spotify. If there's another app that listens to the same hot keys, I think (pretty confident) that it's the last one to register for the hot key.
