Hello I'm reporting this for Homebrew, a package installer for OSX.
mpg321-0.3.2 fails to compile on the current version of OSX because it already defines senum but fails to define a couple of IPV6 variables that occur in Linux but not BSD nor OSX.
These patches fix things, and we appreciate your consideration. I pasted them into a gist.
https://raw.github.com/gist/4084357
2bits @ github
I can confirm that the mpg321.h (senum) patch is needed on OS X 10.7 (and most likely all other OS X releases). I can't say anything about the IPV6 patch. The listed gist no longer works, so here is the patch: