/usr/lib/x86_64-linux-gnu/libgstfft-0.10.so is in libgstreamer-plugins-base0.10-dev 0.10.36-1.1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgstfft-0.10.so.0.25.0