mpeglayer2.cpp

MPEG-4编解码的实现(包括MPEG4视音频编解码)

	switch(scaleselector[LS][i])
	{
	  case 0:scalefactor[LS][0][i]=scalefactorstable[getbits(6)];
		 scalefactor[LS][1][i]=scalefactorstable[getbits(6)];
		 scalefactor[LS][2][i]=scalefactorstable[getbits(6)];
		 break;
	  case 1:scalefactor[LS][0][i]=
		 scalefactor[LS][1][i]=scalefactorstable[getbits(6)];
		 scalefactor[LS][2][i]=scalefactorstable[getbits(6)];
		 break;
	  case 2:scalefactor[LS][0][i]=
		 scalefactor[LS][1][i]=
		 scalefactor[LS][2][i]=scalefactorstable[getbits(6)];
		 break;
	  case 3:scalefactor[LS][0][i]=scalefactorstable[getbits(6)];
		 scalefactor[LS][1][i]=
		 scalefactor[LS][2][i]=scalefactorstable[getbits(6)];
		 break;
	}
      }

      if(inputstereo && (j=bitalloc[RS][i]))
      {
	if(!tableindex)
	{
	  group[RS][i]=grouptableA[j];
	  codelength[RS][i]=codelengthtableA[j];
	  factor[RS][i]=factortableA[j];
	  c[RS][i]=ctableA[j];
	  d[RS][i]=dtableA[j];
	}
	else
	{
	  if(i<=2)
	  {
	    group[RS][i]=grouptableB1[j];
	    codelength[RS][i]=codelengthtableB1[j];
	    factor[RS][i]=factortableB1[j];
	    c[RS][i]=ctableB1[j];
	    d[RS][i]=dtableB1[j];
	  }
	  else
	  {
	    group[RS][i]=grouptableB234[j];
	    if(i<=10)
	    {
	      codelength[RS][i]=codelengthtableB2[j];
	      factor[RS][i]=factortableB2[j];
	      c[RS][i]=ctableB2[j];
	      d[RS][i]=dtableB2[j];
	    }
	    else if(i<=22)
	    {
	      codelength[RS][i]=codelengthtableB3[j];
	      factor[RS][i]=factortableB3[j];
	      c[RS][i]=ctableB3[j];
	      d[RS][i]=dtableB3[j];
	    }
	    else
	    {
	      codelength[RS][i]=codelengthtableB4[j];
	      factor[RS][i]=factortableB4[j];
	      c[RS][i]=ctableB4[j];
	      d[RS][i]=dtableB4[j];
	    }
	  }
	}

	switch(scaleselector[RS][i])
	{
	  case 0 : scalefactor[RS][0][i]=scalefactorstable[getbits(6)];
		   scalefactor[RS][1][i]=scalefactorstable[getbits(6)];
		   scalefactor[RS][2][i]=scalefactorstable[getbits(6)];
		   break;
	  case 1 : scalefactor[RS][0][i]=
		   scalefactor[RS][1][i]=scalefactorstable[getbits(6)];
		   scalefactor[RS][2][i]=scalefactorstable[getbits(6)];
		   break;
	  case 2 : scalefactor[RS][0][i]=
		   scalefactor[RS][1][i]=
		   scalefactor[RS][2][i]=scalefactorstable[getbits(6)];
		   break;
	  case 3 : scalefactor[RS][0][i]=scalefactorstable[getbits(6)];
		   scalefactor[RS][1][i]=
		   scalefactor[RS][2][i]=scalefactorstable[getbits(6)];
		   break;
	}
      }
    }
  }


// Read Sample
  {
    register int i;

    for(int l=0;l<SCALEBLOCK;l++)
    {
      // Read Sample
      for(i=0;i<s;i++)
      {
	if(bitalloc[LS][i])
	{
	  if(group[LS][i])
	  {
	    register const REAL *s;
	    int code=getbits(codelength[LS][i]);

	    code+=code<<1;
            if (code > 2184) {
//printf("fraction LS OverFlow code %d -> 2184 (1)\n", code);
              code=2184;
            }
	    s=group[LS][i]+code;

	    fraction[LS][0][i]=s[0];
	    fraction[LS][1][i]=s[1];
	    fraction[LS][2][i]=s[2];
	  }
	  else
	  {
	    fraction[LS][0][i]=
	      REAL(getbits(codelength[LS][i]))*factor[LS][i]-1.0;
	    fraction[LS][1][i]=
	      REAL(getbits(codelength[LS][i]))*factor[LS][i]-1.0;
	    fraction[LS][2][i]=
	      REAL(getbits(codelength[LS][i]))*factor[LS][i]-1.0;
	  }
	}
	else fraction[LS][0][i]=fraction[LS][1][i]=fraction[LS][2][i]=0.0;

	if(inputstereo && bitalloc[RS][i])
	{
	  if(group[RS][i])
	  {
	    const REAL *s;
	    int code=getbits(codelength[RS][i]);

	    code+=code<<1;
            if (code > 2184) {
//printf("fraction LS OverFlow code %d -> 2184 (2)\n", code);
              code=2184;
            }
	    s=group[RS][i]+code;

	    fraction[RS][0][i]=s[0];
	    fraction[RS][1][i]=s[1];
	    fraction[RS][2][i]=s[2];
	  }
	  else
	  {
	    fraction[RS][0][i]=
	      REAL(getbits(codelength[RS][i]))*factor[RS][i]-1.0;
	    fraction[RS][1][i]=
	      REAL(getbits(codelength[RS][i]))*factor[RS][i]-1.0;
	    fraction[RS][2][i]=
	      REAL(getbits(codelength[RS][i]))*factor[RS][i]-1.0;
	  }
	}
	else fraction[RS][0][i]=fraction[RS][1][i]=fraction[RS][2][i]=0.0;
      }

      for(;i<n;i++)
      {
	if(bitalloc[LS][i])
	{
	  if(group[LS][i])
	  {
	    register const REAL *s;
	    int code=getbits(codelength[LS][i]);

	    code+=code<<1;
	    s=group[LS][i]+code;

	    fraction[LS][0][i]=fraction[RS][0][i]=s[0];
	    fraction[LS][1][i]=fraction[RS][1][i]=s[1];
	    fraction[LS][2][i]=fraction[RS][2][i]=s[2];
	  }
	  else
	  {
	    fraction[LS][0][i]=fraction[RS][0][i]=
	      REAL(getbits(codelength[LS][i]))*factor[LS][i]-1.0;
	    fraction[LS][1][i]=fraction[RS][1][i]=
	      REAL(getbits(codelength[LS][i]))*factor[LS][i]-1.0;
	    fraction[LS][2][i]=fraction[RS][2][i]=
	      REAL(getbits(codelength[LS][i]))*factor[LS][i]-1.0;
	  }
	}
	else fraction[LS][0][i]=fraction[LS][1][i]=fraction[LS][2][i]=
	     fraction[RS][0][i]=fraction[RS][1][i]=fraction[RS][2][i]=0.0;
      }



      //Fraction
      if(outputstereo)
	for(i=0;i<n;i++)
	{
	  if(bitalloc[LS][i])
	  {
	    if(!group[LS][i])
	    {
	      fraction[LS][0][i]=(fraction[LS][0][i]+d[LS][i])*c[LS][i];
	      fraction[LS][1][i]=(fraction[LS][1][i]+d[LS][i])*c[LS][i];
	      fraction[LS][2][i]=(fraction[LS][2][i]+d[LS][i])*c[LS][i];
	    }

	    register REAL t=scalefactor[LS][l>>2][i];
	    fraction[LS][0][i]*=t;
	    fraction[LS][1][i]*=t;
	    fraction[LS][2][i]*=t;
	  }

	  if(bitalloc[RS][i])
	  {
	    if(!group[RS][i])
	    {
	      fraction[RS][0][i]=(fraction[RS][0][i]+d[RS][i])*c[RS][i];
	      fraction[RS][1][i]=(fraction[RS][1][i]+d[RS][i])*c[RS][i];
	      fraction[RS][2][i]=(fraction[RS][2][i]+d[RS][i])*c[RS][i];
	    }

	    register REAL t=scalefactor[RS][l>>2][i];
	    fraction[RS][0][i]*=t;
	    fraction[RS][1][i]*=t;
	    fraction[RS][2][i]*=t;
	  }
	}
      else
	for(i=0;i<n;i++)
	  if(bitalloc[LS][i])
	  {
	    if(!group[LS][i])
	    {
	      fraction[LS][0][i]=(fraction[LS][0][i]+d[LS][i])*c[LS][i];
	      fraction[LS][1][i]=(fraction[LS][1][i]+d[LS][i])*c[LS][i];
	      fraction[LS][2][i]=(fraction[LS][2][i]+d[LS][i])*c[LS][i];
	    }

	    register REAL t=scalefactor[LS][l>>2][i];
	    fraction[LS][0][i]*=t;
	    fraction[LS][1][i]*=t;
	    fraction[LS][2][i]*=t;
	  }

      for(;i<MAXSUBBAND;i++)
	fraction[LS][0][i]=fraction[LS][1][i]=fraction[LS][2][i]=
	fraction[RS][0][i]=fraction[RS][1][i]=fraction[RS][2][i]=0.0;

      for(i=0;i<3;i++)
	subbandsynthesis(fraction[LS][i],fraction[RS][i]);
    }
  }
}