[Vorbis] encoder_example.c Questions

[Daniel Mikusa]

I've been trying to piece my way through the encoder_example.c program 
to better understand how to encode files as ogg/vorbis.  I'm stuck on 
two sections of the code.

This is the first

      /* uninterleave samples */
      for(i=0;i<bytes/4;i++){
        buffer[0][i]=((readbuffer[i*4+1]<<8)|
                      (0x00ff&(int)readbuffer[i*4]))/32768.f;
        buffer[1][i]=((readbuffer[i*4+3]<<8)|
                      (0x00ff&(int)readbuffer[i*4+2]))/32768.f;
      }


This is the second.

    /* vorbis does some data preanalysis, then divvies up blocks for
       more involved (potentially parallel) processing.  Get a single
       block for encoding now */
    while(vorbis_analysis_blockout(&vd,&vb)==1){

      /* analysis, assume we want to use bitrate management */
      vorbis_analysis(&vb,NULL);
      vorbis_bitrate_addblock(&vb);

      while(vorbis_bitrate_flushpacket(&vd,&op)){

        /* weld the packet into the bitstream */
        ogg_stream_packetin(&os,&op);

        /* write out pages (if any) */
        while(!eos){
          int result=ogg_stream_pageout(&os,&og);
          if(result==0)break;
          fwrite(og.header,1,og.header_len,stdout);
          fwrite(og.body,1,og.body_len,stdout);

          /* this could be set above, but for illustrative purposes, I do
             it here (to show that vorbis does know where the stream 
ends) */

          if(ogg_page_eos(&og))eos=1;
        }
      }


Can anyone elaborate on what is happening in these two sections of 
code?  Also if anyone has more / better examples for libvorbis please 
let me know.

Thanks in advance.

Dan Mikusa
dan at trz.cc

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