Have you tested the embed code on the debugging page? I just copy pasted your code and it seemed to work.
Debugging tool showed me the thumbnail properly. However, I open the edit page, click on the “Search Again” link in the Video Thumbnails box but it says “We didn’t find a video thumbnail for this post. (be sure you have saved changes first)”.
I don’t understand what’s wrong. Any suggestions?
I am sorry, I got it now. I was trying to use the video embed field provided by the theme. When I copied the code in to the page, it worked!
I added the custom_video field that comes from the theme into the Custom Field (optional). Now everything works very well.
Thanks for your time.