using VideoInspector it says that the codec is IBM Motion JPEG for the larger of the files (500 meg, so there's definitely something in there!), but it's all blank for the 2nd one.
Dropping power or low battery could definitely cause corruption. Can you define the length of the files recorded? Make them small like 1 minute each which will help in case of low battery or crashing!
Reminds me of the cheap drone I bought a few years ago (that I need to repair), when flying it and getting slightly out of shape, instead of doing something rational I'd panic and cause it to drop out of the sky much worse than if I'd just thought properly for a split second.
This has altitude hold, so in theory just stopping pressing the controls should cause it to hover. Trouble is when it's already carrying speed and you can't work out which way it's facing to slow it down. There's a headless mode (left is always left etc, relative to launch location), but I couldn't seem to get it to engage yesterday. Also a 1 key return button that I only just remembered about.