The biggest dumbest pain in the ass change in macOS High Sierra is the behavior of the media controller keys.
You’ve probably noticed that keys no longer control iTunes/Spotify/Deezer/Vox/etc. They now control video playback in Safari.
It turns out I’m not the only one pissed off about this change, and luckily there’s people like Milan Toth who can do something about it.
He created an app to proxy media key events to iTunes/Spotify/etc. NOTE: right now it only works with psychical buttons ( no TouchBar support )
Pro tip: add the app to your Login Items to have it start at login.