while I was out, your list of things to try faded to white, but I had noted 4 and I tried them. Here is what I got.
costs more than I'm about to risk.
2 mpg to avi was asked to convert a 1.16Mb .MPG file to .AVI
VirtualDub was asked to open it.
It said 'couldn't locate a decompressor for FMP4 (unknown)'
It would also need a VFW codec, but not one like DirectShow uses.
I've previously spent at least 10 hours on the Internet, trying to download said VFW codec but I only got a run-around from clever sales offers for things I didn't want
3 format-factory was given the same task
VirtualDub said 'couldn't locate decompressor for format xvid (unnown)'
also asked for a VFW codec.
4 any-video-converter gave the same result as 3, above.
Maybe I should pension-off VirtualDub and look for an editor that's happy with MPG.