BTW, might be a dumb question, but have you checked the "Recently Deleted" folder in the Photos app?
This folder is new to the Photos app in iOS 8, and it purportedly caches deleted photos and videos for 30 days before purging them. If you haven't cleared out this folder (hit Select, then Delete All), then I would guess that's where all your deleted videos have gone.
This folder is new to the Photos app in iOS 8, and it purportedly caches deleted photos and videos for 30 days before purging them. If you haven't cleared out this folder (hit Select, then Delete All), then I would guess that's where all your deleted videos have gone.