Youtube Video Portfolio Thumbnails?

I’m creating a portfolio from a series of youtube videos. I’ve tried both the embed code and the straight url, but neither is generating a thumbnail. I’m interpreting this line:”Notice: The Preview Image will be the Image set as Featured Image.” to mean that the preview image will automatically populate the Featured image. Am I misreading that? Do I need to create thumbnails for everything?

Thanks, support has been excellent.

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