open and initialize an
OggVorbis_File structure when using a data source other than a file,
when its necessary to modify default file access behavior, or to
initialize a Vorbis decode from a <tt>FILE *</tt> pointer under
Windows where <a href="ov_open.html">ov_open()</a> cannot be used.  It
allows the application to specify custom file manipulation routines
and sets up all the related decoding structures.

<p>Once ov_open_callbacks() has been called, the same
<tt>OggVorbis_File</tt> struct should be passed 