Wordpress says to simply insert a non-hyperlinked URL into your visual editor and the video will appear. When I do this while editing the post the video shows up with a preview. But when previewing or after posting the video isn’t there. I deactivated all plugins and that didn’t fix it. So I switched to the standard WordPress Twenty Sixteen theme and all videos showed up. I then switched back to the standard (non-child) Avien theme and the videos disappeared. I have tried the “Advanced Responsive Video Emdedder” as recommended by the theme, but the video doesn’t show up there, either.