The Unwanted Soundtrack
macOS has a long-standing, deeply integrated behavior designed to facilitate media playback. If you press the “Play/Pause” media key on your keyboard, or if you connect a set of Bluetooth headphones and press the play button on the headset, macOS looks for an active media application. If nothing is currently playing (like a YouTube video in Safari), the operating system automatically assumes you want to listen to your local library and forcefully launches the native Apple Music app (formerly iTunes). This is incredibly frustrating if you use Spotify, or if you were simply trying to pause a video that you accidentally closed a second prior.
Blocking the Play Button Hijack
To retain control over your media keys and stop macOS from automatically launching the Music app when you press play, you must utilize a third-party utility to intercept the command.
Apple does not provide a native setting to disable this hardcoded behavior. The most reliable solution is to install a lightweight, open-source background utility specifically built for this purpose, such as noTunes. You can download noTunes from its GitHub repository. Once installed, it places a small icon (a musical note with a slash through it) in your top menu bar. As long as this utility is running, it intercepts the macOS system call that attempts to open Apple Music. You can now press your media keys or connect your Bluetooth headphones, and the Music app will remain closed, allowing your preferred media player (like Spotify or a web browser) to handle the play command instead.