YouTube Embed does not resize

First of all, I really love the theme, probably one of the best free themes available and its even mostly responsive, which is awesome!

When I embed YouTube videos, they don’t resize when I change the window size. I can make it resize by changing the width to 100%, but then the height don’t change and it makes the video very narrow when resized say for a iPhone or such.

What would I have to do to make the YouTube embed responsive like the rest of the theme?

Thanks in advance!