Both 3.7.0 and 3.7.1 refuse to recognise ffmpeg, even though lib installed in:
/Library/Application Support/audacity/libs
~/Library/Application Support/audacity/libs
libavformat.dylib as a symlink to libavformat.59.16.100.dylib
Restarted both Audacity and the machine.
macOS High Sierra (10.13.6)