Play button on earphones opens iTunes
Not if there's nothing currently playing. Play controls will try to resume the last thing you played that is still running and in memory. If the OS can't find anything to resume, it will default to iTunes.
All media applications are equal; but, iTunes is more equal. 😉
If you are running Sierra, open the terminal and type:
sudo chmod -x /Applications/iTunes.app/Contents/MacOS/iTunes
No more launching iTunes when you press play, since the command stops it from being executable.
However, this will completely disable iTunes:
