Ajouter feuille de style et script
Iframes responsives - Vidéos dans des Iframes responsives

Voir le code ci-dessous
<div style="margin: auto; width:60%">
<div class="iframe-responsive-wrapper">
<img class="iframe-ratio" src="images/ratio800x600.gif" />
<iframe allowfullscreen="" src="https://www.youtube.com/embed/m1vxVhvkHtM?rel=0" width="200" height="150" frameborder="0"></iframe>
</div>
</div>

Voir le code ci-dessous
<div style="margin: auto; width:60%">
<div class="iframe-responsive-wrapper">
<img class="iframe-ratio" src="images/ratio640x360.gif" />
<iframe allowfullscreen="" src="https://www.youtube.com/embed/Nak-j7f6dfE?rel=0" width="160" height="90" frameborder="0"></iframe>
</div>
</div>