This patch adds a check for a null pointer
--- a/src/header_tag.cpp
+++ b/src/header_tag.cpp
@@ -54,7 +54,7 @@
 {
   size_t bytesUsed = ID3_TagHeader::SIZE;
 
-  if (_info->is_extended)
+  if (_info && _info->is_extended)
   {
     bytesUsed += _info->extended_bytes;
   }

This patch by Urs Fleisch prevents crashes when reading VBR MP3 file.
Index: id3lib3.8.3-3.8.3/src/mp3_parse.cpp
===================================================================
--- a/src/mp3_parse.cpp	2009-10-06 23:12:10.381250132 +0200
+++ b/src/mp3_parse.cpp	2009-10-06 23:14:09.545252591 +0200
@@ -465,7 +465,7 @@
   // from http://www.xingtech.com/developer/mp3/
 
   const size_t VBR_HEADER_MIN_SIZE = 8;     // "xing" + flags are fixed
-  const size_t VBR_HEADER_MAX_SIZE = 116;   // frames, bytes, toc and scale are optional
+  const size_t VBR_HEADER_MAX_SIZE = 120;   // frames, bytes, toc and scale are optional
 
   if (mp3size >= vbr_header_offest + VBR_HEADER_MIN_SIZE) 
   {