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/Makefile

@@ -156,7 +156,7 @@ OBJS-$(CONFIG_VCR1_ENCODER)            += vcr1.o
 OBJS-$(CONFIG_VMDAUDIO_DECODER)        += vmdav.o
 OBJS-$(CONFIG_VMDVIDEO_DECODER)        += vmdav.o
 OBJS-$(CONFIG_VMNC_DECODER)            += vmnc.o
-OBJS-$(CONFIG_VORBIS_DECODER)          += vorbis.o vorbis_data.o
+OBJS-$(CONFIG_VORBIS_DECODER)          += vorbis.o vorbis_data.o xiph.o
 OBJS-$(CONFIG_VORBIS_ENCODER)          += vorbis_enc.o vorbis.o vorbis_data.o
 OBJS-$(CONFIG_VP3_DECODER)             += vp3.o
 OBJS-$(CONFIG_VP5_DECODER)             += vp5.o vp56.o vp56data.o

libavcodec/vorbis.c

@@ -33,6 +33,7 @@
 #include "dsputil.h"
 
 #include "vorbis.h"
+#include "xiph.h"
 
 #define V_NB_BITS 8
 #define V_NB_BITS2 11
@@ -1039,7 +1040,7 @@ static int vorbis_decode_init(AVCodecContext *avccontext) {
     uint8_t *header_start[3];
     int header_len[3];
     GetBitContext *gb = &(vc->gb);
-    int i, j, hdr_type;
+    int hdr_type;
 
     vc->avccontext = avccontext;
     dsputil_init(&vc->dsp, avccontext);
@@ -1057,32 +1058,7 @@ static int vorbis_decode_init(AVCodecContext *avccontext) {
         return -1;
     }
 
-    if(headers[0] == 0 && headers[1] == 30) {
-        for(i = 0; i < 3; i++){
-            header_len[i] = *headers++ << 8;
-            header_len[i] += *headers++;
-            header_start[i] = headers;
-            headers += header_len[i];
-        }
-    } else if(headers[0] == 2) {
-        for(j=1,i=0;i<2;++i, ++j) {
-            header_len[i]=0;
-            while(j<headers_len && headers[j]==0xff) {
-                header_len[i]+=0xff;
-                ++j;
-            }
-            if (j>=headers_len) {
-                av_log(avccontext, AV_LOG_ERROR, "Extradata corrupt.\n");
-                return -1;
-            }
-            header_len[i]+=headers[j];
-        }
-        header_len[2]=headers_len-header_len[0]-header_len[1]-j;
-        headers+=j;
-        header_start[0] = headers;
-        header_start[1] = header_start[0] + header_len[0];
-        header_start[2] = header_start[1] + header_len[1];
-    } else {
+    if (ff_split_xiph_headers(headers, headers_len, 30, header_start, header_len) < 0) {
         av_log(avccontext, AV_LOG_ERROR, "Extradata corrupt.\n");
         return -1;
     }

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;
+}

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]);