anchor.diff:    (declare #.utils:*standard-optimize-settings*)
   
     (let ((found-class-symbol (find-symbol (mk-atom-class-name id) :M4A)))
  +
  +    ;(dbg 'find-atom-class id found-class-symbol)
   
       ;; if we found the class name, return the class (to be used for MAKE-INSTANCE)
       (when found-class-symbol
  
positive.code: 
    (let ((top-node
            (tree:at-path (mp4-atoms mp4-file-stream)
                          (list +root+ +mp4-atom-moov+ +mp4-atom-udta+
                                +mp4-atom-meta+ +mp4-atom-ilst+)
                          (lambda (x y)
                            (string= (atom-type (tree:data x)) y)))))
  
  
negative.code:           (tree:find-tree
             (mp4-atoms mp4-file)
             (lambda (x)
               (string= (atom-type (tree:data x)) +itunes-media-header+))))
          (mp4a (tree:find-tree
                 (mp4-atoms mp4-file)
                 (lambda (x)
                   (string= (atom-type (tree:data x)) +itunes-mp4a-codec+))))
          (esds (tree:find-tree
                 (mp4-atoms mp4-file)
                 (lambda (x)
                   (string= (atom-type (tree:data x)) +itunes-elementary-stream-descriptor+)))))
  
      (if (and mdhd mp4a esds)
          (values (tree:data (first mdhd))
  