Why is it that when I drop a mp4 video into the Video Setting it sometimes gives an automatic Thumbnail while other mp4’s don’t.
For those that don’t, I find that if I drop the video itself into the Thumbnail setting it gives me a Thumbnail???
Is this the way it is meant to work.
Finally what is the purpose of the Overlay drop zone in the middle of the Thumbnail or is it there to allow the designer to create his own start right arrow??
Cheers.
Answers some of your questions: Video | RapidWeaver Elements Docs 
Not sure why that would be happening, but could you share a project with us that has an MP4 video where the thumbnail is not being automatically generated?
Don’t do that 
We need to update the Resource drop well to restrict the types of resources it accepts, but we haven’t got to that yet — once we’ve done this you won’t be able to drop a video in to a resource drop well that is expecting an image.
So you can add, for example, a play icon over the top of your thumbnail 
Ben, here are two videos which give the problem and a third middle one which works as expected.
Cheers,
Paul