/usr/lib/x86_64-linux-gnu/libopencv_video.so is in libopencv-video-dev 2.4.9.1+dfsg1-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libopencv_video.so.2.4
/usr/lib/x86_64-linux-gnu/libopencv_video.so.2.4