framing.c

语音滤波源代码

  
  /* continued packet flag? */
  os->header[5]=0x00;
  if((os->lacing_vals[0]&0x100)==0) os->header[5]|=0x01;
  /* first page flag? */
  if(os->b_o_s==0)os->header[5]|=0x02;
  /* last page flag? */
  if(os->e_o_s && os->lacing_fill==vals)os->header[5]|=0x04;
  os->b_o_s=1;

  /* 64 bits of PCM position */
  for(i=6;i<14;i++){
    os->header[i]=(unsigned char)(granule_pos&0xff);
   // granule_pos>>=8;
	granule_pos = granule_pos>>8;
  }

  /* 32 bits of stream serial number */
  {
    long serialno=os->serialno;
    for(i=14;i<18;i++){
      os->header[i]=(unsigned char)(serialno&0xff);
      serialno>>=8;
    }
  }

  /* 32 bits of page counter (we have both counter and page header
     because this val can roll over) */
  if(os->pageno==-1)os->pageno=0; /* because someone called
				     stream_reset; this would be a
				     strange thing to do in an
				     encode stream, but it has
				     plausible uses */
  {
    long pageno=os->pageno++;
    for(i=18;i<22;i++){
      os->header[i]=(unsigned char)(pageno&0xff);
      pageno>>=8;
    }
  }
  
  /* zero for computation; filled in later */
  os->header[22]=0;
  os->header[23]=0;
  os->header[24]=0;
  os->header[25]=0;
  
  /* segment table */
  os->header[26]=(unsigned char)(vals&0xff);
  for(i=0;i<vals;i++)
    bytes+=os->header[i+27]=(unsigned char)(os->lacing_vals[i]&0xff);
  
  /* set pointers in the ogg_page struct */
  og->header=os->header;
  og->header_len=os->header_fill=vals+27;
  og->body=os->body_data+os->body_returned;	//添加地址偏移量
	og->body_len=bytes;
  
  /* advance the lacing data and set the body_returned pointer */
  
  os->lacing_fill-=vals;
  memmove(os->lacing_vals,os->lacing_vals+vals,os->lacing_fill*sizeof(*os->lacing_vals));
  memmove(os->granule_vals,os->granule_vals+vals,os->lacing_fill*sizeof(*os->granule_vals));
  os->body_returned+=bytes;
  
  /* calculate the checksum */
  
  ogg_page_checksum_set(og);//对head[22-26]中数据值作校验,之后输出

  /* done */
  return(1);
}


/* This constructs pages from buffered packet segments.  The pointers
returned are to static buffers; do not free. The returned buffers are
good only until the next call (using the same ogg_stream_state) */

int ogg_stream_pageout(ogg_stream_state *os, ogg_page *og){

  if((os->e_o_s&&os->lacing_fill) ||          /* 'were done, now flush' case */
     os->body_fill-os->body_returned > 4096 ||/* 'page nominal size' case */
     os->lacing_fill>=255 ||                  /* 'segment table full' case */
     (os->lacing_fill&&!os->b_o_s)){          /* 'initial header page' case */
        
    return(ogg_stream_flush(os,og));
  }
  
  /* not enough data to construct a page and not end of stream */
  return(0);
}

int ogg_stream_eos(ogg_stream_state *os){
  return os->e_o_s;
}

/* DECODING PRIMITIVES: packet streaming layer **********************/

/* This has two layers to place more of the multi-serialno and paging
   control in the application's hands.  First, we expose a data buffer
   using ogg_sync_buffer().  The app either copies into the
   buffer, or passes it directly to read(), etc.  We then call
   ogg_sync_wrote() to tell how many bytes we just added.

   Pages are returned (pointers into the buffer in ogg_sync_state)
   by ogg_sync_pageout().  The page is then submitted to
   ogg_stream_pagein() along with the appropriate
   ogg_stream_state* (ie, matching serialno).  We then get raw
   packets out calling ogg_stream_packetout() with a
   ogg_stream_state. */

/* initialize the struct to a known state */
int ogg_sync_init(ogg_sync_state *oy){
  if(oy){
    memset(oy,0,sizeof(*oy));
  }
  return(0);
}

/* clear non-flat storage within */
int ogg_sync_clear(ogg_sync_state *oy){
  if(oy){
    if(oy->data)_ogg_free(oy->data);
    ogg_sync_init(oy);
  }
  return(0);
}

int ogg_sync_destroy(ogg_sync_state *oy){
  if(oy){
    ogg_sync_clear(oy);
    _ogg_free(oy);
  }
  return(0);
}

char *ogg_sync_buffer(ogg_sync_state *oy, long size){

  /* first, clear out any space that has been previously returned */
  if(oy->returned){//清除缓存区空间内值
    oy->fill-=oy->returned;
    if(oy->fill>0)
      memmove(oy->data,oy->data+oy->returned,oy->fill);
    oy->returned=0;
  }

  if(size>oy->storage-oy->fill){
    /* We need to extend the internal buffer */
    long newsize=size+oy->fill+4096; /* an extra page to be nice */
		//扩展内部缓存
    if(oy->data)
      oy->data=_ogg_realloc(oy->data,newsize);
    else
      oy->data=_ogg_malloc(newsize);
    oy->storage=newsize;
  }

  /* expose a segment at least as large as requested at the fill mark */
  return((char *)oy->data+oy->fill);
}

int ogg_sync_wrote(ogg_sync_state *oy, long bytes){
  if(oy->fill+bytes>oy->storage)return(-1);
  oy->fill+=bytes;
  return(0);
}

/* sync the stream.  This is meant to be useful for finding page
   boundaries.

   return values for this:
  -n) skipped n bytes
   0) page not ready; more data (no bytes skipped)
   n) page synced at current location; page length n bytes
   
*/

long ogg_sync_pageseek(ogg_sync_state *oy,ogg_page *og){
  unsigned char *page=oy->data+oy->returned;
  unsigned char *next;
  long bytes=oy->fill-oy->returned;
  
  if(oy->headerbytes==0){
    int headerbytes,i;
    if(bytes<27)return(0); /* not enough for a header */
    
    /* verify capture pattern */
    if(memcmp(page,"OggS",4))goto sync_fail;
    
    headerbytes=page[26]+27;
    if(bytes<headerbytes)return(0); /* not enough for header + seg table */
    
    /* count up body length in the segment table */
    
    for(i=0;i<page[26];i++)
      oy->bodybytes+=page[27+i];
    oy->headerbytes=headerbytes;
  }
  
  if(oy->bodybytes+oy->headerbytes>bytes)return(0);
  
  /* The whole test page is buffered.  Verify the checksum */
  {
    /* Grab the checksum bytes, set the header field to zero */
    char chksum[4];
    ogg_page log;
    
    memcpy(chksum,page+22,4);
    memset(page+22,0,4);
    
    /* set up a temp page struct and recompute the checksum */
    log.header=page;
    log.header_len=oy->headerbytes;
    log.body=page+oy->headerbytes;
    log.body_len=oy->bodybytes;
    ogg_page_checksum_set(&log);
    
    /* Compare */
    if(memcmp(chksum,page+22,4)){
      /* D'oh.  Mismatch! Corrupt page (or miscapture and not a page
	 at all) */
      /* replace the computed checksum with the one actually read in */
      memcpy(page+22,chksum,4);
      
      /* Bad checksum. Lose sync */
      goto sync_fail;
    }
  }
  
  /* yes, have a whole page all ready to go */
  {
    unsigned char *page=oy->data+oy->returned;
    long bytes;

    if(og){
      og->header=page;
      og->header_len=oy->headerbytes;
      og->body=page+oy->headerbytes;
      og->body_len=oy->bodybytes;
    }

    oy->unsynced=0;
    oy->returned+=(bytes=oy->headerbytes+oy->bodybytes);
    oy->headerbytes=0;
    oy->bodybytes=0;
    return(bytes);
  }
  
 sync_fail:
  
  oy->headerbytes=0;
  oy->bodybytes=0;
  
  /* search for possible capture */
  next=memchr(page+1,'O',bytes-1);
  if(!next)
    next=oy->data+oy->fill;

  oy->returned=next-oy->data;
  return(-(next-page));
}

/* sync the stream and get a page.  Keep trying until we find a page.
   Supress 'sync errors' after reporting the first.

   return values:
   -1) recapture (hole in data)
    0) need more data
    1) page returned

   Returns pointers into buffered data; invalidated by next call to
   _stream, _clear, _init, or _buffer */

int ogg_sync_pageout(ogg_sync_state *oy, ogg_page *og){

  /* all we need to do is verify a page at the head of the stream
     buffer.  If it doesn't verify, we look for the next potential
     frame */

  for(;;){
    long ret=ogg_sync_pageseek(oy,og);//从oy中读取数据头和数据到og中去
    if(ret>0){
      /* have a page */
      return(1);
    }
    if(ret==0){
      /* need more data */
      return(0);
    }
    
    /* head did not start a synced page... skipped some bytes */
    if(!oy->unsynced){
      oy->unsynced=1;
      return(-1);
    }

    /* loop. keep looking */

  }
}

/* add the incoming page to the stream state; we decompose the page
   into packet segments here as well. */

int ogg_stream_pagein(ogg_stream_state *os, ogg_page *og){
  unsigned char *header=og->header;
  unsigned char *body=og->body;
  long           bodysize=og->body_len;
  int            segptr=0;

  int version=ogg_page_version(og);
  int continued=ogg_page_continued(og);
  int bos=ogg_page_bos(og);
  int eos=ogg_page_eos(og);
  ogg_int64_t granulepos=ogg_page_granulepos(og);
  int serialno=ogg_page_serialno(og);
  long pageno=ogg_page_pageno(og);
  int segments=header[26];
  
  /* clean up 'returned data' */
  {
    long lr=os->lacing_returned;
    long br=os->body_returned;

    /* body data */
    if(br){
      os->body_fill-=br;
      if(os->body_fill)
	memmove(os->body_data,os->body_data+br,os->body_fill);
      os->body_returned=0;
    }

    if(lr){
      /* segment table */
      if(os->lacing_fill-lr){
	memmove(os->lacing_vals,os->lacing_vals+lr,
		(os->lacing_fill-lr)*sizeof(*os->lacing_vals));
	memmove(os->granule_vals,os->granule_vals+lr,
		(os->lacing_fill-lr)*sizeof(*os->granule_vals));
      }
      os->lacing_fill-=lr;
      os->lacing_packet-=lr;
      os->lacing_returned=0;
    }
  }

  /* check the serial number */
  if(serialno!=os->serialno)return(-1);
  if(version>0)return(-1);

  _os_lacing_expand(os,segments+1);

  /* are we in sequence? */
  if(pageno!=os->pageno){
    int i;

    /* unroll previous partial packet (if any) */
    for(i=os->lacing_packet;i<os->lacing_fill;i++)
      os->body_fill-=os->lacing_vals[i]&0xff;
    os->lacing_fill=os->lacing_packet;

    /* make a note of dropped data in segment table */
    if(os->pageno!=-1){
      os->lacing_vals[os->lacing_fill++]=0x400;
      os->lacing_packet++;
    }
  }

  /* are we a 'continued packet' page?  If so, we may need to skip
     some segments */