gistfile1.rb

  def music_on_hold
    output = play! "/path/to/music.wav", :repeat_times => 0

    hid = call.on_joined do
      output.stop! if output.executing?
    end

    begin
      yield.tap do
        output.stop! if output.executing?
      end
    ensure
      call.unregister_handler :event, hid
    end
  end