/usr/lib/x86_64-linux-gnu/libmpg123.so.0 is in libmpg123-0 1.20.1-2+deb8u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libmpg123.so.0.40.3
/usr/lib/x86_64-linux-gnu/libmpg123.so.0.40.3