??? how would that affect responsiveness?

778 x 438 would be upsized to 1138 x 640 but it would keep aspect ratio.

EDIT: I found a solution

There are two ways to input a video…

either by ID: t-kWDBxV6yA

or by EMBED code:
< iframe width=”778″ height=”438″ src=”//www.youtube.com/embed/t-kWDBxV6yA” frameborder=”0″ allowfullscreen></iframe >

If I use ID, then a page with sidebar, 778 x 438 will have black bars on the sides of the video as it’s trying to fit into 778 x 389 so instead of squeezing the video, it makes black bars.

If i use the embed code, it looks perfect, no black side bars, 778 x 438

if i use full width, it gives the video almost perfect size, 1138 x 641 instead of 1138 x 640… but that’s way better than using the ID.

will get you a screenshot to show what I mean.