Thumbnails for MP4 Video

I have tried to read through the posts here about thumbnails, but didn’t find my exact question answered.

I have a bunch of MP4 video (.m4v extension) and have used a program to embed a jpg for the video thumbnail into each one.  Windows Explorer shows the file with the proper jpg file that is embedded.

The WDTV Live does not display the thumbnails.

To test one, I put a jpg file with the exact same name as one of the video files in the same directory.  WDTV Live then showed the thumbnail.

So, it appears that the device will not show an embedded jpg as the thumbnail.

My question, is that just how it is, or is it possible that I have something setup wrong?

I can’t remember specifically, but I think it only works for movies via USB, as part of the media library function.