/usr/lib/x86_64-linux-gnu/libmpcdec.so is in libmpcdec-dev 2:0.1~r459-4.1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libmpcdec.so.6.1.0
/usr/lib/x86_64-linux-gnu/libmpcdec.so.6.1.0