Factorise id3v2 header parsing from mp3.c to be shared

Patch by Alex Converse ( alex converse gmail com )

Originally committed as revision 16615 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/id3v2.h

@@ -0,0 +1,35 @@
+/*
+ * ID3v2 header parser
+ * Copyright (c) 2003 Fabrice Bellard
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVFORMAT_ID3V2_H
+#define AVFORMAT_ID3V2_H
+
+#include <stdint.h>
+
+#define ID3v2_HEADER_SIZE 10
+
+/**
+ * Detects ID3v2 Header.
+ * @buf must be ID3v2_HEADER_SIZE byte long
+ */
+int ff_id3v2_match(const uint8_t *buf);
+
+#endif /* AVFORMAT_ID3V2_H */