Shouldering on, here is additional information developed this afternoon:
a) The device I need to "export" video from is a KT&C OMNI 960 digital recorder, great for saving the output from, in this instance, four video surveillance cameras;
b) This OMNI has a UBS port that accepts a thumb drive for "exporting." The OMNI is able to format a drive in either of two "file systems:" FAT32 (default) or NTFS;
c) I recently experimented by "exporting" files onto the thumb drive using each format. The NTFS formatted disk "was not readable by this computer."
d) The FAT32 formatted disk WAS readable by the MacBook, but the exported files, which had now acquired an ".mp4" suffix, could not be opened by the computer's QuickTime (default) application.
e) BUT, in another life, I must have downloaded the VLC application. This VLC app was pleased to open the ".mp4" movie file, and allowed me to watch the video recording, made on the OMNI, on my computer.
This is as far as I've gotten, which is a lot further than i was a day ago. I will eventually wrestle with this some more, and am hopeful there is some way to use part of this ".mp4" movie in my computer's iMovie application. If anyone in the community has any shortcuts for how to make that happen, please bring 'em on!