The communication with the TagLib library is done via a tiny program written in C emms-print-metadata.c. To compile emms-print-metadata invoke:
make emms-print-metadata
The resultant binary will be installed when you invoke:
make install as in See Compiling Emms.
It is of course also possible to install only the emms-print-metadata binary where your system can find and execute it without installing all of Emms via the make command.
Once the binary is available load emms-info-libtag and make it
the only info function with (note that if you have caching
enabled you may have to delete the existing cache and repopulate it in
order to see the TagLib data):
(require 'emms-info-libtag)
(setq emms-info-functions '(emms-info-libtag))