For those of you running a UNV type mini DVR (sold by some other companies under another name) for thermal scopes such as older ATNs, Armasights, IR Defense/Trijicons who have experienced recording a file that would not play, due to a problem such a not switching off properly or some other disruption, I have found a solution that will work at least some of the time.
The DVR creates an AVI format file. If the file is there (saved) but will not play, what I have found is that using a file converter such as https://www.videoconverterfactory.com/
and converting to an MP4 file will result in a viewable file that can be edited and shared just like the original should have been.
I have had problems twice since adopting this file converter to use with some video files and both times when I have tried to covert the errant AVI hunting video file, it has converted successfully.https://www.videoconverterfactory.com/
is a free program and in the free format (haven't tried the purchased version, yet), it is a bit slow, but works very nicely. The free version will handle 720 resolution, which is greater than the DVR's 640 resolution, so nothing will be lost in terms of resolution.
Other converters may work. I don't know. What I do know is that this works, at least some of the time, and is free. If you have files that won't play or edit from your hunts, you might give this program a try.