Displaying video embed at 100% width?

So I have noticed that right now videos aren't embedded at 100% width.

It's smaller than pictures:

How to set this up so that videos would also be embedded at 100% width?

Maybe there's an option that I'm missing?

If not, where should I look for in plugin php file to make it 100% width and auto height?

I really need this.

The video is a bit small right now imo.

Thanks in advance.

R.