Use absolute filenames and include some comments:
# my first filename file /mnt/share/file-1.wav # my second filename including whitespace file '/mnt/share/file 2.wav' # my third filename including whitespace plus single quote file '/mnt/share/file 3'\''.wav'
Allow for input format auto-probing, use safe filenames and set the duration of the first file:
ffconcat version 1.0 file file-1.wav duration 20.0 file subdir/file-2.wav