Hello Fred,
Both Video importer plugin rely on Xuggler library which is, unfortunately, not very stable or not anymore maintained :-/
I also have some video here making it crashes but hopefully it does happen rarely.
Do you think you can upload the video somewhere so i can test it and see if we can somehow make Xuggler to open it with specific settings ? Thanks.
As for a video converter, you may try FFMpeg :
https://www.ffmpeg.org/Best,
- Stephane