I am becoming familiar with all of this. Being forced too. I like using ffmpeg to do as much of my work with videos as it can be done in a matter of seconds versus minutes if using kdenlive.
Big problem with using the concatenation option I like to use is that all the files list have to have the same codec. If one of the files from A119e is has its speed altered with ffmpeg, it effects "TAG:compatible_brands"
Files on my A119 go from a "isomavc1mp42" to a "isomiso2mp41" if use "-filter:v "setpts=0.25*PTS" -an " (which speeds a file to 4 times its speed). My A119 and A118c2 have different "compatible brands", codec_tag_string and codec_tags.
Anyway, I found a FAST way to re-encode files from my four different cameras, some with speed altering, so they are consistent. I can now get my files to concatenate with ffmpeg.