Comment # 1 on bug 1058195 from Luigi Baldoni

https://build.opensuse.org/package/binary/openSUSE:Leap:42.3/gstreamer-plugins-ugly?arch=x86_64&filename=gstreamer-plugins-ugly-1.8.3-4.1.x86_64.rpm&repository=standard
shows a dependency on libmpg123.so.0, does ldd
/usr/lib64/gstreamer-1.0/libgstmpg123.so tell you otherwise?