Why are the photos and videos distorted on the margins?(YI LITE Action Camera)

a. YI Lite Action Camera uses a 150° degree ultra-wide-angle lens resulting in some distortion.

b. You can go to "Settings -> LDC" and turn on "Lens Distortion Correction." Doing so will make the photos or videos look normal . When you turn "Lens Distortion Correction" off, the photos or videos will appear distorted again.