id3v2: use a named constant instead of 0x02

Originally committed as revision 25902 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/id3v2.c

@@ -211,7 +211,7 @@ void ff_id3v2_parse(AVFormatContext *s, int len, uint8_t version, uint8_t flags)
             }else
                 tlen = get_size(s->pb, 4);
             tflags = get_be16(s->pb);
-            tunsync = tflags & 0x02;
+            tunsync = tflags & ID3v2_FLAG_UNSYNCH;
         } else {
             get_buffer(s->pb, tag, 3);
             tag[3] = 0;

libavformat/id3v2.h

@@ -33,6 +33,11 @@
  */
 #define ID3v2_DEFAULT_MAGIC "ID3"
 
+#define ID3v2_FLAG_DATALEN     0x0001
+#define ID3v2_FLAG_UNSYNCH     0x0002
+#define ID3v2_FLAG_ENCRYPTION  0x0004
+#define ID3v2_FLAG_COMPRESSION 0x0008
+
 /**
  * Detect ID3v2 Header.
  * @param buf   must be ID3v2_HEADER_SIZE byte long