Use can use width: 0; height: 0; position: absolute; and border: 0;
So the updated code will be!
<iframe src="https://www.youtube.com/embed/X18mUlDddCc?autoplay=1" style="position: absolute;width:0;height:0;border:0;"></iframe>
Added:
style="position: absolute; width:0; height:0; border:0;"
It will hide it, make media to play in the background and it will also collapse it space!
Updated Fiddle
http://jsfiddle.net/ygkvbphs/