libmpg123.so.0 was removed from gstreamer-plugins-ugly
https://build.opensuse.org/package/view_file/openSUSE:Leap:42.3/gstreamer-plugins-ugly/gstreamer-plugins-ugly.changes?expand=1
but it wasn't included in any other of the gstreamer packages (I just checked
gstreamer and gstreamer-plugins-base)
this breaks mp3 support in most applications that use gstreamer as a backend
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-ugly-plugins/html/gst-plugins-ugly-plugins-plugin-mpg123.html
strangely enough the 32 bit rpm gstreamer-plugins-ugly-32bit still includes the
32 bit shared object libmpg123.so.0 but that is useless with 64bit apps like
amarok
packman still packages libmpg123.so.0 inside gstreamer-plugins-ugly that's why
mp3 playback works with a vendor change to packman
afaik the mp3 patents have ended and mp3 support should be available out of the
box