public OggVorbisInfo(IntPtr ptr)
 {
     info = (VorbisInfo)Marshal.PtrToStructure(ptr, typeof(VorbisInfo));
 }
 static internal extern void vorbis_info_clear(ref VorbisInfo vi);          // vorbis_info *, to dealloc
 internal OggVorbisInfo(VorbisInfo info)
 {
     this.info = info;
 }
 static internal extern void vorbis_info_init(ref VorbisInfo vi);          // vorbis_info *, to output allocated pointer