+/* used to track pcm position without actually performing decode.
+ Useful for sequential 'fast forward' */
+int vorbis_synthesis_trackonly(vorbis_block *vb,ogg_packet *op){
+ vorbis_dsp_state *vd=vb->vd;
+ private_state *b=vd->backend_state;
+ vorbis_info *vi=vd->vi;
+ codec_setup_info *ci=vi->codec_setup;
+ oggpack_buffer *opb=&vb->opb;
+ int mode;
+
+ /* first things first. Make sure decode is ready */
+ _vorbis_block_ripcord(vb);
+ oggpack_readinit(opb,op->packet,op->bytes);
+
+ /* Check the packet type */
+ if(oggpack_read(opb,1)!=0){
+ /* Oops. This is not an audio data packet */
+ return(OV_ENOTAUDIO);
+ }
+
+ /* read our mode and pre/post windowsize */
+ mode=oggpack_read(opb,b->modebits);
+ if(mode==-1)return(OV_EBADPACKET);
+
+ vb->mode=mode;
+ if(!ci->mode_param[mode]){
+ return(OV_EBADPACKET);
+ }
+
+ vb->W=ci->mode_param[mode]->blockflag;
+ if(vb->W){
+ vb->lW=oggpack_read(opb,1);
+ vb->nW=oggpack_read(opb,1);
+ if(vb->nW==-1) return(OV_EBADPACKET);
+ }else{
+ vb->lW=0;
+ vb->nW=0;
+ }
+
+ /* more setup */
+ vb->granulepos=op->granulepos;
+ vb->sequence=op->packetno;
+ vb->eofflag=op->e_o_s;
+
+ /* no pcm */
+ vb->pcmend=0;
+ vb->pcm=NULL;