Some MP4 files are invisible to PlayOn MyMedia - a bypass

Videos recorded from YouTube, using Free YouTube Download software, are NOT seen by the Roku PlayOn app. The folder holding them is not even visible. PLEX has the same problem.
The problem videos can be identified immediately by choosing File / View / Large icons. The good ones show a scene from the video - the bad ones just show a PLAY icon.
The good ones also have more information in “details” in the Property view. The bad ones have no name, or details about the audio or video.
I installed PLEX thinking it might not have the problem - but it also has it.
My solution is to convert them from mp4 to mp4. It puts the right information in the new output file. Takes a bit of electricity - but that works. I really need a faster conversion tool!