extract vorbis header spliting code into a reusable function

Original thread:
Date: Thu, 22 Mar 2007 20:23:08 -0400
Subject: [Ffmpeg-devel] [PATCH] Theora in MKV (GSoC '07 Qualification)

Originally committed as revision 8505 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/xiph.c

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2007  FFmpeg Project
+ *
+ * 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
+ */
+
+#include "xiph.h"
+
+int ff_split_xiph_headers(uint8_t *extradata, int extradata_size,
+                          int first_header_size, uint8_t *header_start[3],
+                          int header_len[3])
+{
+    int i, j;
+
+    if (AV_RB16(extradata) == first_header_size) {
+        for (i=0; i<3; i++) {
+            header_len[i] = AV_RB16(extradata);
+            extradata += 2;
+            header_start[i] = extradata;
+            extradata += header_len[i];
+        }
+    } else if (extradata[0] == 2) {
+        for (i=0,j=1; i<2; i++,j++) {
+            header_len[i] = 0;
+            for (; j<extradata_size && extradata[j]==0xff; j++) {
+                header_len[i] += 0xff;
+            }
+            if (j >= extradata_size)
+                return -1;
+
+            header_len[i] += extradata[j];
+        }
+        header_len[2] = extradata_size - header_len[0] - header_len[1] - j;
+        extradata += j;
+        header_start[0] = extradata;
+        header_start[1] = header_start[0] + header_len[0];
+        header_start[2] = header_start[1] + header_len[1];
+    } else {
+        return -1;
+    }
+    return 0;
+}