change extradata format for vorbis

Originally committed as revision 4235 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/utils.c

@@ -1015,3 +1015,17 @@ int avcodec_thread_init(AVCodecContext *s, int thread_count){
     return -1;
 }
 #endif
+
+unsigned int av_xiphlacing(unsigned char *s, unsigned int v)
+{
+    unsigned int n = 0;
+
+    while(v >= 0xff) {
+        *s++ = 0xff;
+        v -= 0xff;
+        n++;
+    }
+    *s = v;
+    n++;
+    return n;
+}