MAC OS convert mp4 to mp3
Open Finder
cd to directory with mp4 files
select files you want to be converted
use right mouse button to open context menu
goto / select Dienste ( Services )
choose "Ausgewählte Videodateien codieren"
Window will open which allows to select output format
select Audio … and run.
all selected mp4 files will remain
and be converted to m4v files.
rename them to mp3 by selecting all wanted files
use right mousebutton and goto rename / umbenennen