Version 1.7 now includes a 'usb-sync.sh' script that will copy all media on a USB pen drive to the /var/lib/minidlna folder. 

subsequant runs will only sync the changes to /var/lib/minidlna folder

It uses rsync to copy only changes from the pen drive.

so only new media files added on the pen drive will be copied after the first copy has happened.

to run, log into cockpit and type 'cd  /home/pi/pi-setup'

then type 'sudo ./usb-sync.sh'

example running in cockpit's terminal window :-