Bringing CKeditor, embedded content (e.g. iframe) and responsive design together
You can override youtube videos using CSS and media queries. Infact, most videos from Youtube, Vimeo etc are all available in an iframe. In projects in the past, I allow clients to just copy and paste an embed field into a ckeditor field wherever they like, at any dimension they please.

But, once the screen width is reduced to mobile, my CSS takes over, and resizes the video to fit the mobile template, to reduce overlapping, and fix any issue with video height.

E.g.

@media only screen and (max-width: 767px) {

.field-name-body iframe     {width:100%;height:200px;}

}


Is that what you mean, or I have I not understood the question?