Hi,

This enhances our emacs-emms package so that it can retrieve the
metadata from FLAC and MP3 files. It also references GNU find
explicitly.

Here's how I tested it:

1. Backup (rename) any existing ~/.emacs.d/emms directory to get rid of
any cached playlist.
2. Make sure you have a collections of a few FLAC, Ogg and MP3 files
under ~/Music.
3. Add the following config to your .emacs file:
--8<---------------cut here---------------start------------->8---
;;; EMMS
(require 'emms-info-metaflac)
(require 'emms-setup)
(emms-all)
(emms-default-players)
(add-to-list 'emms-info-functions #'emms-info-metaflac)
(setq emms-source-file-directory-tree-function
      #'emms-source-file-directory-tree-find)
(setq emms-source-file-default-directory "~/Music/")
--8<---------------cut here---------------end--------------->8---
4. With the patch applied, run:
--8<---------------cut here---------------start------------->8---
./pre-inst-env guix environment --pure --ad-hoc emacs emacs-emms
emacs
--8<---------------cut here---------------end--------------->8---
5. Create the playlist from your default music directory:
M-x emms-add-directory-tree RET ~/Music RET
6. Finally, lauch EMMS with M-x emms and observe that the playlist was
correctly generated based on the files' metadata.

Thank you,

Maxim