/usr/lib/x86_64-linux-gnu/libffmpegthumbnailer.so is in libffmpegthumbnailer-dev 2.0.10-0.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libffmpegthumbnailer.so.4
/usr/lib/x86_64-linux-gnu/libffmpegthumbnailer.so.4