18:36 antoine@macbook ~/videolan/vlc-build% ./vlc ~/media/music/Greenday/American\ Idiot/01\ -\ American\ Idiot.mp3 --sout '#transcode{acodec=mpga,ab=32,channels=1}:std{access=file,mux=raw,dst=/tmp/a.mp3}' -vvv -I dummy --no-media-library

(with pre 9107e1e0 builds you need to add --sout-mono-downmix to the command line)