/*FIRST AND BEST WAY (?) IS AS FOLLOWS:.*/

iframe{
width: 50vw;
height: 28.125vw;
}

/*SECOND AND CLUNKY AND HARD TO WORK WITH OTHER ELEMENTS WAY IS Wrap the video in class="video-container" then add this to stylsheet and adjust:*/

.video-container {
	position: relative;
	padding-bottom: 56.25%;
	/*huge paddding above is only way this works, may have to adjust masx height and overflow of whatever element this is contained in to prevent page from becoming too tall*/
	height: 0;
}
.video-container iframe{
	position: absolute;
	top: 0;
	left: 0;
	width: 100%; /*or a fixed pixel height*/
	height: 100%;
}