Graeme
my apologies for the confusion. I believe I had a bad link, and you should now be able to download the FMV 1.4 manual from http://esriurl.com/FMV14manual. This is public and you should not be challenged for a login to Box; if that is not working, please let me know.
To clarify expectations: FMV 1.4 does not have new features since FMV 1.3.2. FMV is using the add-in architecture for ArcGIS, so we have to create a new build for each version of ArcMap. FMV 1.3.2 is not compatible with ArcMap 10.6, so FMV 1.4 was rebuilt for 10.6, but unfortunately we did not add any new video formats.
On the topic of video formats, one common issue is a desire to play *.MOV format. As noted in the FAQ (http://esriurl.com/FMVFAQ), *MOV format files are typically encoded as *.h264, so if you simply make a copy (for backup) and rename your video file *.h264, it should work.
Let us know if this does not resolve your questions.
Cody B