If you want to display a subset of your collection (such as a directory of 80s music, only avi files, etc.) then you can extend the Browser by defining “filters”.
(emms-browser-make-filter "all" 'ignore)
Set "all" as the default filter:
(emms-browser-set-filter (assoc "all" emms-browser-filters))
Show all files (no streamlists, etc):
(emms-browser-make-filter "all-files" (emms-browser-filter-only-type 'file))
Show only tracks in one folder:
(emms-browser-make-filter "80s" (emms-browser-filter-only-dir "~/Mp3s/80s"))
Show all tracks played in the last month:
(emms-browser-make-filter "last-month" (emms-browser-filter-only-recent 30))
After executing the above commands, you can use M-x emms-browser-show-all, emms-browser-show-80s, etc to toggle between different collections. Alternatively you can use '<' and '>' to cycle through the available filters.
The second argument to make-filter is a function which returns t if a single track should be filtered. You can write your own filter functions to check the type of a file, etc.
Show only tracks not played in the last year:
(emms-browser-make-filter "not-played" (lambda (track) (not (funcall (emms-browser-filter-only-recent 365) track))))
Show all files that are not in the pending directory:
(emms-browser-make-filter "all" (lambda (track) (or (funcall (emms-browser-filter-only-type 'file) track) (not (funcall (emms-browser-filter-only-dir "~/Media/pending") track)))))