@michaelkammes Oh yes, it was a tough video file, I also tested ffmpeg/avidemux/vlc and more method found online. Asking on Mastodon was my last desperate attempt.
The solution: using a command line tool named untrunc https://github.com/ponchio/untrunc , RinCat in the thread fixed the mp4 with it.
Yes, this is the segment 'F' and crashed after 30min afair , I usually try to not exceed recording session of 1h.