I tried to build sox on MacOS with MP3 support. A few months back; I forget the details, but it either would not build that way, or afterwards it failed to accept MP3.
So I tried what was in the instructions about pointing an environment variable to lame. That didn't work either. I need to concatenate thousands of 1-3 second files into 21 larger files and I would rather not have to first convert them to .wav
I have two versions of lame, a recent "standard" and a custom built for a particular application.