encode.c

mpeg文件格式类型的文档

   int jsbound = fr_ps->jsbound;
   int i,j,k;
 
   for (i=0;i<sblimit;i++) for (k=0;k<stereo;k++)
     if (bit_alloc[k][i])  putbits(bs,scfsi[k][i],2);
 
   for (i=0;i<sblimit;i++) for (k=0;k<stereo;k++)
     if (bit_alloc[k][i])  /* above jsbound, bit_alloc[0][i] == ba[1][i] */
        switch (scfsi[k][i]) {
           case 0: for (j=0;j<3;j++)
                     putbits(bs,scalar[k][j][i],6);
                   break;
           case 1:
           case 3: putbits(bs,scalar[k][0][i],6);
                   putbits(bs,scalar[k][2][i],6);
                   break;
           case 2: putbits(bs,scalar[k][0][i],6);
        }
}
 
/*=======================================================================\
|                                                                        |
|      The following routines are done after the masking threshold       |
| has been calculated by the fft analysis routines in the Psychoacoustic |
| model. Using the MNR calculated, the actual number of bits allocated   |
| to each subband is found iteratively.                                  |
|                                                                        |
\=======================================================================*/
 
/************************************************************************
*
* I_bits_for_nonoise  (Layer I)
* II_bits_for_nonoise (Layer II)
*
* PURPOSE:Returns the number of bits required to produce a
* mask-to-noise ratio better or equal to the noise/no_noise threshold.
*
* SEMANTICS:
* bbal = # bits needed for encoding bit allocation
* bsel = # bits needed for encoding scalefactor select information
* banc = # bits needed for ancillary data (header info included)
*
* For each subband and channel, will add bits until one of the
* following occurs:
* - Hit maximum number of bits we can allocate for that subband
* - MNR is better than or equal to the minimum masking level
*   (NOISY_MIN_MNR)
* Then the bits required for scalefactors, scfsi, bit allocation,
* and the subband samples are tallied (#req_bits#) and returned.
*
* (NOISY_MIN_MNR) is the smallest MNR a subband can have before it is
* counted as 'noisy' by the logic which chooses the number of JS
* subbands.
*
* Joint stereo is supported.
*
************************************************************************/

static double snr[18] = {0.00, 7.00, 11.00, 16.00, 20.84,
                         25.28, 31.59, 37.75, 43.84,
                         49.89, 55.93, 61.96, 67.98, 74.01,
                         80.03, 86.05, 92.01, 98.01};

int I_bits_for_nonoise(perm_smr, fr_ps)
double FAR perm_smr[2][SBLIMIT];
frame_params *fr_ps;
{
   int i,j,k;
   int stereo  = fr_ps->stereo;
   int sblimit = fr_ps->sblimit;
   int jsbound = fr_ps->jsbound;
   int req_bits = 0;
 
   /* initial b_anc (header) allocation bits */
   req_bits = 32 + 4 * ( (jsbound * stereo) + (SBLIMIT-jsbound) );
 
   for(i=0; i<SBLIMIT; ++i)
     for(j=0; j<((i<jsbound)?stereo:1); ++j) {
       for(k=0;k<14; ++k)
         if( (-perm_smr[j][i] + snr[k]) >= NOISY_MIN_MNR)
           break; /* we found enough bits */
         if(stereo == 2 && i >= jsbound)     /* check other JS channel */
           for(;k<14; ++k)
             if( (-perm_smr[1-j][i] + snr[k]) >= NOISY_MIN_MNR) break;
         if(k>0) req_bits += (k+1)*SCALE_BLOCK + 6*((i>=jsbound)?stereo:1);
   }
   return req_bits;
}
 
/***************************** Layer II  ********************************/
 
int II_bits_for_nonoise(perm_smr, scfsi, fr_ps)
double FAR perm_smr[2][SBLIMIT];
unsigned int scfsi[2][SBLIMIT];
frame_params *fr_ps;
{
   int sb,ch,ba;
   int stereo  = fr_ps->stereo;
   int sblimit = fr_ps->sblimit;
   int jsbound = fr_ps->jsbound;
   al_table *alloc = fr_ps->alloc;
   int req_bits = 0, bbal = 0, berr = 0, banc = 32;
   int maxAlloc, sel_bits, sc_bits, smp_bits;
static int sfsPerScfsi[] = { 3,2,1,2 };    /* lookup # sfs per scfsi */

   /* added 92-08-11 shn */
   if (fr_ps->header->error_protection) berr=16; else berr=0; 
 
   for (sb=0; sb<jsbound; ++sb)
     bbal += stereo * (*alloc)[sb][0].bits;
   for (sb=jsbound; sb<sblimit; ++sb)
     bbal += (*alloc)[sb][0].bits;
   req_bits = banc + bbal + berr;
 
   for(sb=0; sb<sblimit; ++sb)
     for(ch=0; ch<((sb<jsbound)?stereo:1); ++ch) {
       maxAlloc = (1<<(*alloc)[sb][0].bits)-1;
       sel_bits = sc_bits = smp_bits = 0;
       for(ba=0;ba<maxAlloc-1; ++ba)
         if( (-perm_smr[ch][sb] + snr[(*alloc)[sb][ba].quant+((ba>0)?1:0)])
             >= NOISY_MIN_MNR)
            break;      /* we found enough bits */
       if(stereo == 2 && sb >= jsbound) /* check other JS channel */
         for(;ba<maxAlloc-1; ++ba)
           if( (-perm_smr[1-ch][sb]+ snr[(*alloc)[sb][ba].quant+((ba>0)?1:0)])
               >= NOISY_MIN_MNR)
             break;
       if(ba>0) {
         smp_bits = SCALE_BLOCK * ((*alloc)[sb][ba].group * (*alloc)[sb][ba].bits);
         /* scale factor bits required for subband */
         sel_bits = 2;
         sc_bits  = 6 * sfsPerScfsi[scfsi[ch][sb]];
         if(stereo == 2 && sb >= jsbound) {
           /* each new js sb has L+R scfsis */
           sel_bits += 2;
           sc_bits  += 6 * sfsPerScfsi[scfsi[1-ch][sb]];
         }
         req_bits += smp_bits+sel_bits+sc_bits;
       }
   }
   return req_bits;
}
 
/************************************************************************
*
* I_main_bit_allocation   (Layer I)
* II_main_bit_allocation  (Layer II)
*
* PURPOSE:For joint stereo mode, determines which of the 4 joint
* stereo modes is needed.  Then calls *_a_bit_allocation(), which
* allocates bits for each of the subbands until there are no more bits
* left, or the MNR is at the noise/no_noise threshold.
*
* SEMANTICS:
*
* For joint stereo mode, joint stereo is changed to stereo if
* there are enough bits to encode stereo at or better than the
* no-noise threshold (NOISY_MIN_MNR).  Otherwise, the system
* iteratively allocates less bits by using joint stereo until one
* of the following occurs:
* - there are no more noisy subbands (MNR >= NOISY_MIN_MNR)
* - mode_ext has been reduced to 0, which means that all but the
*   lowest 4 subbands have been converted from stereo to joint
*   stereo, and no more subbands may be converted
*
*     This function calls *_bits_for_nonoise() and *_a_bit_allocation().
*
************************************************************************/
 
void I_main_bit_allocation(perm_smr, bit_alloc, adb, fr_ps)
double FAR perm_smr[2][SBLIMIT];
unsigned int bit_alloc[2][SBLIMIT];
int *adb;
frame_params *fr_ps;
{
   int  noisy_sbs;
   int  mode, mode_ext, lay, i;
   int  rq_db, av_db = *adb;
static  int init = 0;
 
   if(init == 0) {
     /* rearrange snr for layer I */
     snr[2] = snr[3];
     for (i=3;i<16;i++) snr[i] = snr[i+2];
     init = 1;
   }
 
   if((mode = fr_ps->actual_mode) == MPG_MD_JOINT_STEREO) {
     fr_ps->header->mode = MPG_MD_STEREO;
     fr_ps->header->mode_ext = 0;
     fr_ps->jsbound = fr_ps->sblimit;
     if(rq_db = I_bits_for_nonoise(perm_smr, fr_ps) > *adb) {
       fr_ps->header->mode = MPG_MD_JOINT_STEREO;
       mode_ext = 4;           /* 3 is least severe reduction */
       lay = fr_ps->header->lay;
       do {
          --mode_ext;
          fr_ps->jsbound = js_bound(lay, mode_ext);
          rq_db = I_bits_for_nonoise(perm_smr, fr_ps);
       } while( (rq_db > *adb) && (mode_ext > 0));
       fr_ps->header->mode_ext = mode_ext;
     }    /* well we either eliminated noisy sbs or mode_ext == 0 */
   }
   noisy_sbs = I_a_bit_allocation(perm_smr, bit_alloc, adb, fr_ps);
}
 
/***************************** Layer II  ********************************/
 
void II_main_bit_allocation(perm_smr, scfsi, bit_alloc, adb, fr_ps)
double FAR perm_smr[2][SBLIMIT];
unsigned int scfsi[2][SBLIMIT];
unsigned int bit_alloc[2][SBLIMIT];
int *adb;
frame_params *fr_ps;
{
   int  noisy_sbs, nn;
   int  mode, mode_ext, lay;
   int  rq_db, av_db = *adb;
 
   if((mode = fr_ps->actual_mode) == MPG_MD_JOINT_STEREO) {
     fr_ps->header->mode = MPG_MD_STEREO;
     fr_ps->header->mode_ext = 0;
     fr_ps->jsbound = fr_ps->sblimit;
     if((rq_db=II_bits_for_nonoise(perm_smr, scfsi, fr_ps)) > *adb) {
       fr_ps->header->mode = MPG_MD_JOINT_STEREO;
       mode_ext = 4;           /* 3 is least severe reduction */
       lay = fr_ps->header->lay;
       do {
         --mode_ext;
         fr_ps->jsbound = js_bound(lay, mode_ext);
         rq_db = II_bits_for_nonoise(perm_smr, scfsi, fr_ps);
       } while( (rq_db > *adb) && (mode_ext > 0));
       fr_ps->header->mode_ext = mode_ext;
     }    /* well we either eliminated noisy sbs or mode_ext == 0 */
   }
   noisy_sbs = II_a_bit_allocation(perm_smr, scfsi, bit_alloc, adb, fr_ps);
}
 
/************************************************************************
*
* I_a_bit_allocation  (Layer I)
* II_a_bit_allocation (Layer II)
*
* PURPOSE:Adds bits to the subbands with the lowest mask-to-noise
* ratios, until the maximum number of bits for the subband has
* been allocated.
*
* SEMANTICS:
* 1. Find the subband and channel with the smallest MNR (#min_sb#,
*    and #min_ch#)
* 2. Calculate the increase in bits needed if we increase the bit
*    allocation to the next higher level
* 3. If there are enough bits available for increasing the resolution
*    in #min_sb#, #min_ch#, and the subband has not yet reached its
*    maximum allocation, update the bit allocation, MNR, and bits
    available accordingly
* 4. Repeat until there are no more bits left, or no more available
*    subbands. (A subband is still available until the maximum
*    number of bits for the subband has been allocated, or there
*    aren't enough bits to go to the next higher resolution in the
    subband.)
*
************************************************************************/
 
int I_a_bit_allocation(perm_smr, bit_alloc, adb, fr_ps) /* return noisy sbs */
double FAR perm_smr[2][SBLIMIT];
unsigned int bit_alloc[2][SBLIMIT];
int *adb;
frame_params *fr_ps;
{
   int i, k, smpl_bits, scale_bits, min_sb, min_ch, oth_ch;
   int bspl, bscf, ad, noisy_sbs, done = 0, bbal ;
   double mnr[2][SBLIMIT], small;
   char used[2][SBLIMIT];
   int stereo  = fr_ps->stereo;
   int sblimit = fr_ps->sblimit;
   int jsbound = fr_ps->jsbound;
   al_table *alloc = fr_ps->alloc;
static char init= 0;
static int banc=32, berr=0;
 
   if (!init) {
      init = 1;
      if (fr_ps->header->error_protection) berr = 16;  /* added 92-08-11 shn */
   }
   bbal = 4 * ( (jsbound * stereo) + (SBLIMIT-jsbound) );
   *adb -= bbal + berr + banc;
   ad= *adb;
 
   for (i=0;i<SBLIMIT;i++) for (k=0;k<stereo;k++) {
     mnr[k][i]=snr[0]-perm_smr[k][i];
     bit_alloc[k][i] = 0;
     used[k][i] = 0;
   }
   bspl = bscf = 0;
 
   do  {
     /* locate the subband with minimum SMR */
     small = mnr[0][0]+1;    min_sb = -1; min_ch = -1;
     for (i=0;i<SBLIMIT;i++) for (k=0;k<stereo;k++)
       /* go on only if there are bits left */
       if (used[k][i] != 2 && small > mnr[k][i]) {
         small = mnr[k][i];
         min_sb = i;  min_ch = k;
       }
     if(min_sb > -1) {   /* there was something to find */
       /* first step of bit allocation is biggest */
       if (used[min_ch][min_sb])  { smpl_bits = SCALE_BLOCK; scale_bits = 0; }
       else                       { smpl_bits = 24; scale_bits = 6; }
       if(min_sb >= jsbound)        scale_bits *= stereo;
 
       /* check to see enough bits were available for */
       /* increasing resolution in the minimum band */
 
       if (ad >= bspl + bscf + scale_bits + smpl_bits) {
         bspl += smpl_bits; /* bit for subband sample */
         bscf += scale_bits; /* bit for scale factor */
         bit_alloc[min_ch][min_sb]++;
         used[min_ch][min_sb] = 1; /* subband has bits */
         mnr[min_ch][min_sb] = -perm_smr[min_ch][min_sb]
                               + snr[bit_alloc[min_ch][min_sb]];
         /* Check if subband has been fully allocated max bits */
         if (bit_alloc[min_ch][min_sb] ==  14 ) used[min_ch][min_sb] = 2;
       }
       else            /* no room to improve this band */
         used[min_ch][min_sb] = 2; /*   for allocation anymore */
       if(stereo == 2 && min_sb >= jsbound) {
         oth_ch = 1-min_ch;  /* joint-st : fix other ch */
         bit_alloc[oth_ch][min_sb] = bit_alloc[min_ch][min_sb];
         used[oth_ch][min_sb] = used[min_ch][min_sb];
         mnr[oth_ch][min_sb] = -perm_smr[oth_ch][min_sb]
                               + snr[bit_alloc[oth_ch][min_sb]];
       }
     }
   } while(min_sb>-1);     /* i.e. still some sub-bands to find */

   /* Calculate the number of bits left, add on to pointed var */
   ad -= bspl+bscf;
   *adb = ad;

   /* see how many channels are noisy */
   noisy_sbs = 0; small = mnr[0][0];
   for(k=0; k<stereo; ++k) {
     for(i = 0; i< SBLIMIT; ++i) {
       if(mnr[k][i] < NOISY_MIN_MNR)   ++noisy_sbs;
       if(small > mnr[k][i])           small = mnr[k][i];
     }
   }
   return noisy_sbs;
}

/***************************** Layer II  ********************************/
 
int II_a_bit_allocation(perm_smr, scfsi, bit_alloc, adb, fr_ps)
double FAR perm_smr[2][SBLIMIT];
unsigned int scfsi[2][SBLIMIT];
unsigned int bit_alloc[2][SBLIMIT];
int *adb;
frame_params *fr_ps;
{
   int i, min_ch, min_sb, oth_ch, k, increment, scale, seli, ba;
   int bspl, bscf, bsel, ad, noisy_sbs, bbal=0;
   double mnr[2][SBLIMIT], small;
   char used[2][SBLIMIT];
   int stereo  = fr_ps->stereo;