I finally found time to build a distribution on github. My mov2gpx program is now available here. It is, of course, open source. This version 1 works on the Nextbase 312GW and on the SG9665GC. I thought that it would probably work on the other Nextbase models, at least, so I asked Nextbase for samples of output. I was taken aback to find that they are different. Apart from one outlier, it looks easy to adjust mov2gpx to handle those cameras as well, and version 2 will do that - when I find time to write it.
To get a feel for what mov2gpx does, try the pdf version of the man page, although there is a strong clue in the name.
There are precompiled binaries in the releases directory for a variety of operating systems.