Using Sox, ffmpeg (python audio tools) in mac

Installing Sox

download zip file from Sox page and unzip it.

After unzip, register PATH in ~/.zshrc(or ~/.bashrc) 
export PATH=$PATH:/path/to/sox-dir 
Then you can use sox commands like sox, play.

Installing ffmpeg

brew install ffmpeg

Using Sox

Changing mp3 to flac

ffmpeg -i input.mp3 output.flac

good webpage converting audio format