Youtube video in nested symbol?

I need to add a youtube video inside of a nested symbol (two layers deep).  Is this possible?  The video would essentially need to load into what would be a makeshift lightbox (like the screenshot below). Other pages where I've got youtube videos working I've used the following code:

if(document.getElementById('Stage_intro-video').children.length == 0){

var v = document.createElement('iframe');

  v.setAttribute('width', '1000');

  v.setAttribute('height', '562');

  v.setAttribute('src', 'https://www.youtube.com/embed/XXXXXXXX?rel=0&controls=0&autoplay=1');

  v.setAttribute('frameborder', '0');

document.getElementById('Stage_intro-video').appendChild(v);

}