It is inverted in the last seconds because the camera goes upside down so it is consistent with a round planet. the curvature is clearly visible in this video and you can tell it is not a fish eye lens due to features on the land below and the skydivers having zero distortion. Can not wait to see FE'rs explain this in detail
I have sky dived twice and did not see any curvature. Certainly not with my eyes. You only go between 4-5km max. Hardly enough area to see far enough out that you could witness a curvature (if there is one
)
Keep trying though. It's been fun
Agreed, not only is it not high enough, but the
goPro camera used has too much
barrel distortion to be useful for the tiny curve that might be there.
Lens distortion can be minimised by selecting a frame where the horizon goes through the centre of the image and preferably with the horizon as horizontal as possible.
Here are three adjacent frames that were the best that I could find:
 GoPro HD skydiving footage test at Lodi Parachute Center, horizon above centre (false convex curve) | |  GoPro HD skydiving footage test at Lodi Parachute Center, horizon close to centre (no curve) | |  GoPro HD skydiving footage test at Lodi Parachute Center, horizon below centre (concave curve) |
The horizon curvature is so slight till you get to say 100,000 ft that great care is needed to observe it.
This one, taken from a flat earther's video at 121,000 ft, shows enough to be convincing:
Losing Your Ride at 121,000 Feet - A Preview Indiana Caver at 0.17 secsSo just watch lens distortion or these flat earthers will be down on you "like a ton of bricks".