There are two (three) things that, in my experience, can cause EMMS to fail to get tags from mp3info.
Your $PATH variable in Emacs is different from your shell's $PATH variable. This can happen especially on Mac OS X gui emacs. You can check Emacs' path variable with
M-x getenv RET, and choosing PATH from a list. A solution is to use the package
exec-path-from-shell, which can be installed via the melpa package manager in emacs. If installed manually you'll need
(require 'exec-path-from-shell). In any case, after installing, add
(exec-path-from-shell-initialize) to your init file. Do
which mp3info or whatever to verify whether the executable lies within Emacs' $PATH.
Install EMMS via git and not via ELPA. It appears that some users (i.e., myself) found that elpa EMMS does not interface with any tag program, but that cleaning the elpa EMMS out and installing from the git repository does work.
(3.) I don't think this is a problem for the original question, but
mp3info only works with id3v1 tags, whereas many MP3s may only have id3v2.* tags. I suggest you use libtag for compatability with all tags and other non-MP3 file formats. To setup with libtag follow instructions in my other answer about this.
To keep mp3info follow the same instructions but remove the libtag stuff from the init configuration. I have done that below:
(add-to-list 'load-path "~/.emacs.d/lisp/emms/lisp/");;add the emms elisp path
;;emms configuration ;;; elisp comment ;)
(require 'emms) ;;; load emms from "~/.emacs.d/lisp/emms/lisp/"
;;; i.e., the core functionality
(require 'emms-setup);;; load some functions that will set some preferences
;;; it's worth looking at this file
(emms-all) ;;; load all stable features of emms, defined in emms-setup
(emms-default-players);; load a list of default players (like mplayer) installed defined in emms-setup
(setq emms-source-file-default-directory "/Volumes/Seabeam HD/Music/")
;;; below is a nice key command for toggling the music browser
(autoload 'emms-smart-browse "emms-browser.el" "Browse with EMMS" t)
(global-set-key [(f7)] 'emms-smart-browse)