Samsung .um4 audio/video files: how to play them?

I've had for some time a hard drive that came with my Samsung SMART TV circa 2016 which had 4K video content.
The TV just recently just stopped being able to play them. I'll contact Samsung later to see if they can fix this.
So I hooked the drive up to my PC thinking I could find some package somewhere i.e
Media Player that could play it. I discovered that all the files had a .um4 extension. Along with these
.um4 file was a matching file with a .smi extension. The smi files were a few kilo bytes but the um4 files were
in the 10 megabytes size.

Anyone have an idea on how to decode these files?

Open the um4 file with MediaInfo. If that recognizes the file format, then you should be able to play it with MPC-HC. If not, you are out of luck.