Import Vorbis seeking improvements from Tremor SVN.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@21841 a1c6a512-1295-4272-9138-f99709370657

apps/codecs/libtremor/info.c

@@ -232,6 +232,31 @@ static int _vorbis_unpack_books(vorbis_info *vi,oggpack_buffer *opb){
   return(OV_EBADHEADER);
 }
 
+/* Is this packet a vorbis ID header? */
+int vorbis_synthesis_idheader(ogg_packet *op){
+  oggpack_buffer opb;
+  char buffer[6];
+
+  if(op){
+    oggpack_readinit(&opb,op->packet);
+
+    if(!op->b_o_s)
+      return(0); /* Not the initial packet */
+
+    if(oggpack_read(&opb,8) != 1)
+      return 0; /* not an ID header */
+
+    memset(buffer,0,6);
+    _v_readstring(&opb,buffer,6);
+    if(memcmp(buffer,"vorbis",6))
+      return 0; /* not vorbis */
+
+    return 1;
+  }
+
+  return 0;
+}
+
 /* The Vorbis header is in three packets; the initial small packet in
    the first page that identifies basic parameters, a second packet
    with bitstream comments and a third packet that holds the

apps/codecs/libtremor/ivorbiscodec.h

@@ -166,6 +166,7 @@ extern int      vorbis_block_clear(vorbis_block *vb);
 extern void     vorbis_dsp_clear(vorbis_dsp_state *v);
 
 /* Vorbis PRIMITIVES: synthesis layer *******************************/
+extern int      vorbis_synthesis_idheader(ogg_packet *op);
 extern int      vorbis_synthesis_headerin(vorbis_info *vi,vorbis_comment *vc,
 					  ogg_packet *op);