(ql:quickload '(cl-out123 cl-mpg123))

(defun play-mp3 (file &key driver output (buffer-size T))
  (let* ((file (cl-mpg123:connect (cl-mpg123:make-file file :buffer-size buffer-size)))
         (out  (cl-out123:connect (cl-out123:make-output driver :device output))))
    (format T "Playback device ~a / ~a" (cl-out123:driver out) (cl-out123:device out))
    (multiple-value-bind (rate channels encoding) (cl-mpg123:file-format file)
      (format T "Input format ~a Hz, ~a channels, ~a encoded." rate channels encoding)
      (cl-out123:start out :rate rate :channels channels :encoding encoding))
    (unwind-protect
         (loop with buffer = (cl-mpg123:buffer file)
               for read = (cl-mpg123:process file)
               for played = (cl-out123:play out buffer read)
               while (< 0 read)
               do (when (/= played read)
                    (format T "Playback is not catching up with input by ~a bytes."
                            (- read played))))
      (cl-out123:stop out)
      (cl-out123:disconnect out)
      (cl-mpg123:disconnect file))))