How to get a which marquee span is onStart marquee

I want to change a label when announcement 1 is on screen then label 1 is shown ... after that announcement 2 is is on and label 1 is hidden and label 2 is shown.

<marquee id="marquee_element" class="marquee_element">
        <span class="notification_marquee first "></span>
        <span class="notification_marquee second not_sec"></span>
        <span class="notification_marquee third not_3rd"></span>
        <span class="notification_marquee fourth not_4th"></span>
        <span class="notification_marquee fifth not_5th"></span>
 </marquee>

these are announcements,

and below are the labels

<div class="col-md-2 col-xs-12 annoucements annoucements-style">
    <div class="text-center annoucements-text">
      <span id="an_label_1" class="an_label not_fst"></span>
      <span id="an_label_2" class="an_label hidden not_sec"></span>
      <span id="an_label_3" class="an_label hidden not_3rd"></span>
      <span id="an_label_4" class="an_label hidden not_4th"></span>
      <span id="an_label_5" class="an_label hidden not_5th"></span>
    </div>
  </div>

via Chebli Mohamed