I said "Tube".
OK, New Plan™!
First I tried the Embed Video module, and it works, it is very not responsive.
Then I tried the YouTube module, and make a YouTube Video content type. This works great, and, I have a shitload of content types already.
So, I'm adding the field to Blog Posts. This is going to give me an advantage later, me thinks, as I think of using Paragraphs for things. More on that later.