Just copy the iFrame code from Youtube and paste it into the hiTuber Stack and the Youtube video is responsive. It'll look something like this:
Want to make it autoplay? Add ?rel=0&autoplay=1 just after the https-adress before quote:
Hi. I'm DeFliGra. A long time developer of RapidWeaver Stacks Addons called Stacks. I've been an even longer time user of RapidWeaver and came on board when RapidWeaver 3 was released.