+It is called by wxSoundFileStream to prepare the specific file loader
+to prepare itself to play the file. Actually, this includes reading
+headers and setting the various parameters of the sound format.
+This should not be called by an external user but it should be
+implemented when you inherit wxSoundFileStream to build a new codec.
+
+It must return when the file is identified and the parameters have
+been set. In all other cases, you must return FALSE.