ffmpeg -f avfoundation -i :0 out.wav

ffmpeg version 3.3.9 Copyright © 2000-2018 the FFmpeg developers
built with gcc 9.3.0 (GCC)
configuration: prefix=/usr/local/ffmpeg339
libavutil 55. 58.100 / 55. 58.100
libavcodec 57. 89.100 / 57. 89.100
libavformat 57. 71.100 / 57. 71.100
libavdevice 57. 6.100 / 57. 6.100
libavfilter 6. 82.100 / 6. 82.100
libswscale 4. 6.100 / 4. 6.100
libswresample 2. 7.100 / 2. 7.100
Unknown input format: 'avfoundation’