Chrome: video de reproducción automática modal al cargar

Buenos días,

So i set up a modal to open a embeded youtube video and to autoplay when it opens, this works great in firefox but in chrome it starts autoplaying the moment the page is loaded even without the modal being triggered, so you just end up with background music playing without knowing from where.

<div class="small-12 medium-3 large-3 columns video-box">
  <a href="#" data-reveal-id="vtc" data-reveal>
     <img src="img/video/vid1.jpg">
  </a>
</div>

<div id="vtc" class="reveal-modal medium" data-reveal>
  <div class="flex-video">
    <iframe width="560" height="315" src="//www.youtube.com/embed/-pjadXDB0zo?rel=1"   frameborder="0" allowfullscreen></iframe>
  </div>
</div>

Is this a bug or is there a way around it?

Muchas Gracias