  This paper proposes a vision-based method for video sky replacement and
harmonization, which can automatically generate realistic and dramatic sky
backgrounds in videos with controllable styles. Different from previous sky
editing methods that either focus on static photos or require inertial
measurement units integrated in smartphones on shooting videos, our method is
purely vision-based, without any requirements on the capturing devices, and can
be well applied to either online or offline processing scenarios. Our method
runs in real-time and is free of user interactions. We decompose this artistic
creation process into a couple of proxy tasks including sky matting, motion
estimation, and image blending. Experiments are conducted on videos diversely
captured in the wild by handheld smartphones and dash cameras, and show high
fidelity and good generalization of our method in both visual quality and
lighting/motion dynamics. Our code and animated results are available at
\url{https://jiupinjia.github.io/skyar/}.
