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.h

@@ -0,0 +1,38 @@
+/*
+ * 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 "common.h"
+
+/**
+ * Splits a single extradata buffer into the three headers that most
+ * Xiph codecs use. (e.g. Theora and Vorbis)
+ * Works both with Matroska's packing and lavc's packing.
+ *
+ * @param[in] extradata The single chunk that combines all three headers
+ * @param[in] extradata_size The size of the extradata buffer
+ * @param[in] first_header_size The size of the first header, used to
+ * differentiate between the Matroska packing and lavc packing.
+ * @param[out] header_start Pointers to the start of the three separate headers.
+ * @param[out] header_len The sizes of each of the three headers.
+ * @return On error a negative value is returned, on success zero.
+ */
+int ff_split_xiph_headers(uint8_t *extradata, int extradata_size,
+                          int first_header_size, uint8_t *header_start[3],
+                          int header_len[3]);