mpeg: fixed xing header parsing for files with CRC protection (#1059)

git-svn-id: http://svn.code.sf.net/p/qmmp-dev/code/trunk/qmmp@9487 90c681e8-e032-0410-971d-27865f9a5e38

1 files changed, 16 insertions, 1 deletions

diff --git a/src/plugins/Input/mpeg/decoder_mad.cpp b/src/plugins/Input/mpeg/decoder_mad.cpp
index 59b77c71d..7f3ca4f93 100644
--- a/src/plugins/Input/mpeg/decoder_mad.cpp
+++ b/src/plugins/Input/mpeg/decoder_mad.cpp
@@ -128,8 +128,23 @@ bool DecoderMAD::findXingHeader(struct mad_bitptr ptr, unsigned int bitlen)
         return false;
 
     quint32 xing_magic = mad_bit_read(&ptr, 32);
+    bitlen -= 32;
+
     if(xing_magic != XING_MAGIC && xing_magic != XING_MAGIC2)
-        return false;
+    {
+        /*
+         * Due to an unfortunate historical accident, a Xing VBR tag may be
+         * misplaced in a stream with CRC protection. We check for this by
+         * assuming the tag began two octets prior and the high bits of the
+         * following flags field are always zero.
+         */
+
+        if(xing_magic != ((quint64(XING_MAGIC) << 16) & 0xffffffffL) && xing_magic != ((quint64(XING_MAGIC2) << 16) & 0xffffffffL))
+            return false;
+
+        mad_bit_skip(&ptr, 16);
+        bitlen += 16;
+    }
 
     m_xing.flags = mad_bit_read(&ptr, 32);
     bitlen -= 64;