@Neigh: 1st of all thanks for the the code and template. I just embedded a video, and noticed that in Preview the bit after PASTE ID", i.e. starting from frameborder=“0” was visible as text, i.e. it was not part of the video embed code.
I deleted it, and the video still works, so to me it seems that bit from frameborder on is superfluous. Now, your expertise is waaaaay above my modest knowledge, so I cannot believe you would have added extraneous stuff, so please help me understand.