I decided to install the K-Lite Mega Codec Pack to see if this sorts out my problem - sadly, no such luck! Even K-Lite's Media Player Classic fails! Note: I am now using Unifab v2.0.2.1 and am still getting the problem.
Thinking, perhaps, that the new K-Lite pack might improve the Unifab conversion's compatibility, I regenerated some test files with different format settings, and tried to play them with different video players. I found:
1. Selecting any Samsung Galaxy device (S4, S7, Tab Pro) has only H.264 (same as source) as the video codec option, and the .mp4 file is unplayable by all 8 of the video players (including such good stand-bys as VLC Media Player, GOM Player & Windows Media Player).
2. Selecting a generic MP4-Full HD 1920x1080 format offers 4 codec options. Selecting H.264 (same as source) allowed me to play the converted file with GOM Player, K-Lite's MPC-HC, SMPlayer Media Player, and Windows Media Player.
3. As for 2, but selecting the MPEG4 codec, all my 8 players work (the others not listed so far are: Films & TV, Media Player, VLC Media Player, and Power DVD 22).
There seems to be something not right with Unifab's H.264 convert codec. It was all right in DVDFab 12 (including for Samsung Galaxy devices), so what's changed/broken?
Paul.