Well, I've never done it, but it should be easy.

Easy enough to test doing it anyway.

You just want to put a video bar under the thumb?

Open a thumb in photoshop. Open the video bar. make sure the video bar is the desired size.

Start recording an action.

Increase the canvas size by the height of the video bar, anchoring the canvas at the top. This will create a blank space the height of the bar under the thumb.

copy the video bar and paste it into the thumb. move it to the desired position.

Stop the recording.

That should then do the exact same thing to any number of thumbs - assuming they are all the same size. I would run it off the screen, not directed at a folder - but you could add an extra part of the action, that lets you run it on a folder, that opens the required video bar, copys it, and closes it again. Easier to open it once and run it off the screen.

("off the screen" means to run it on files that you have dragged and dropped into photoshop - basically, to run it on opened thumbs.)

You could do the same thing to paste a thumb inside a video player frame.

I haven't tested this, but feel certain that with a bit of trial and error it will work.

groan - I guess I should test it before saying it's possible, hahahha.