+ /* 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;
+
+ return(0);
+}
+
+long vorbis_packet_blocksize(vorbis_info *vi,ogg_packet *op){
+ codec_setup_info *ci=vi->codec_setup;
+ oggpack_buffer opb;
+ int mode;
+
+ 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);
+ }
+
+ {
+ int modebits=0;
+ int v=ci->modes;
+ while(v>1){
+ modebits++;
+ v>>=1;
+ }
+
+ /* read our mode and pre/post windowsize */
+ mode=oggpack_read(&opb,modebits);
+ }
+ if(mode==-1 || !ci->mode_param[mode])return(OV_EBADPACKET);
+ return(ci->blocksizes[ci->mode_param[mode]->blockflag]);
+}
+
+int vorbis_synthesis_halfrate(vorbis_info *vi,int flag){
+ /* set / clear half-sample-rate mode */
+ codec_setup_info *ci=vi->codec_setup;
+
+ /* right now, our MDCT can't handle < 64 sample windows. */
+ if(ci->blocksizes[0]<=64 && flag)return -1;
+ ci->halfrate_flag=(flag?1:0);
+ return 0;
+}
+
+int vorbis_synthesis_halfrate_p(vorbis_info *vi){
+ codec_setup_info *ci=vi->codec_setup;
+ return ci->halfrate_flag;
+}