Here's some HTML code that'll lazy load YouTube videos. There are better solutions for doing this site-wide, but this is good for just one or two videos. Code courtesy of CSS-Tricks.com
<iframe
width="560"
height="315"
src="https://www.youtube.com/embed/Y8Wp3dafaMQ&autoplay=1"
srcdoc="<style>*{padding:0;margin:0;overflow:hidden}html,body{height:100%}img,span{position:absolute;width:100%;top:0;bottom:0;margin:auto}span{height:1.5em;text-align:center;font:48px/1.5 sans-serif;color:white;text-shadow:0 0 0.5em black}</style><a href=https://www.youtube.com/embed/Y8Wp3dafaMQ?autoplay=1><img src=https://img.youtube.com/vi/Y8Wp3dafaMQ/hqdefault.jpg alt='Video The Dark Knight Rises: What Went Wrong? – Wisecrack Edition'><span>▶</span></a>"
frameborder="0"
allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture"
allowfullscreen
title="The Dark Knight Rises: What Went Wrong? – Wisecrack Edition"
></iframe>