I’m not sure if there is a built in function in MC, but I used smartlists to find duplicates:
Step 1:
Create a smartlist with all files which should be in scope. Lets call this “All”
Step 2:
Then create a smartlist to look for duplicates using the following rule:
Playlist: All Duplicates: [Artist],[Name],[Duration],[File Size]
Lets calls this “Dup1”.
Of course the attributes for the “Duplicates” modifier depend on your definition of “duplicate”. I added “Duration” because sometimes there are different versions (remixes) of the same song and “File Size” because sometime different encoder setting could have been used for the same source to produce the output (e.g. encoder, bitrate,..) . The resulting smartlist gives you all files which appear at least twice.
Step 3:
(Optional) Shrink the list to get only one representative of each file:
Playlist: Dup1 No Duplicates: [Artist],[Name],[Duration],[File Size]