Background Music is a macOS audio utility to automatically pause your music, set individual apps' volumes and record system audio.
brew install sscotth/backgroundmusic/background-music
Or brew tap sscotth/backgroundmusic and then brew install background-music.
Or install via URL:
brew install https://raw.githubusercontent.com/sscotth/homebrew-backgroundmusic/master/Casks/background-music.rb
brew help, man brew or check Homebrew's documentation.