For more information on viewport-adaptive motion compensation, see:
A. Regensky, C. Herglotz and A. Kaup, "A Novel Viewport-Adaptive Motion
Compensation Technique for Fisheye Video," ICASSP 2021 - 2021 IEEE
International Conference on Acoustics, Speech and Signal Processing
(ICASSP), 2021, pp. 1565-1569, doi: 10.1109/ICASSP39728.2021.9413576.