I can tell because I hear the fans on my Power Mac Quad G5 kick up to full speed.
Sample clearly indicates that it's spinning through all the media folders and stat-ing all the files (with plenty of calls to getdirentries in between).
On the Mac, one should use fsevents for notification of changes to a directory tree instead of polling like this (wasting electricity as well).
Windows has file system change notifications also and Linux has inotify/dnotify as well.
Polling is badness.