So, youtube gives out the iframe tag as follows:
<iframe width="560" height="315" src="https://www.youtube.com/embed/2EIeUlvHAiM" frameborder="0" allowfullscreen></iframe>
In my case, i just changed it to width="100%" and left the rest as is. It's not the most elegant solution (after all, in different devices you'll get weird ratios) But the video itself does not get deformed, just the frame.