getpic.c

视频的h263解码

      if (Mode == MODE_INTER_Q || Mode == MODE_INTRA_Q) {
        /* Read DQUANT if necessary */

        if (syntax_arith_coding) {
          DQUANT_index = decode_a_symbol(cumf_DQUANT);
          DQUANT = dquanttab[DQUANT_index] - 2; 
          quant +=DQUANT;
          if (trace)
            printf("DQUANT Index: %d DQUANT %d \n",DQUANT_index, DQUANT);
        }
        else {
          DQUANT = getbits(2);
          quant += DQ_tab[DQUANT];
          if (trace) {
            printf("DQUANT (");
            printbits(DQUANT,2,2);
            printf("): %d = %d\n",DQUANT,DQ_tab[DQUANT]);
          }
        }

        if (quant > 31 || quant < 1) {
          if (!quiet)
            printf("Quantizer out of range: clipping\n");
          quant = mmax(1,mmin(31,quant));
          /* could set fault-flag and resync here */
        }
      }

      /* motion vectors */
      if (Mode == MODE_INTER || Mode == MODE_INTER_Q || 
          Mode == MODE_INTER4V || pb_frame) {

        if (Mode == MODE_INTER4V) { startmv = 1; stopmv = 4;}
        else { startmv = 0; stopmv = 0;}

        for (k = startmv; k <= stopmv; k++) {
          if (syntax_arith_coding) {
            mvx_index = decode_a_symbol(cumf_MVD);
            mvx = mvdtab[mvx_index];
            mvy_index = decode_a_symbol(cumf_MVD);
            mvy = mvdtab[mvy_index];
            if (trace)
              printf("mvx_index: %d mvy_index: %d \n", mvy_index, mvx_index);
          }
          else {
            mvx = getTMNMV();
            mvy = getTMNMV();
          }

          pmv0 = find_pmv(xpos,ypos,k,0);
          pmv1 = find_pmv(xpos,ypos,k,1);
          mvx = motion_decode(mvx, pmv0);
          mvy = motion_decode(mvy, pmv1);
          if (trace) {
            printf("mvx: %d\n", mvx);
            printf("mvy: %d\n", mvy);
          }
          /* Check mv's to prevent seg.faults when error rate is high */
          if (!mv_outside_frame) {
            bsize = k ? 8 : 16;
            offset = k ? (((k-1)&1)<<3) : 0;
            /* checking only integer component */
            if ((xpos<<4) + (mvx/2) + offset < 0 ||
        (xpos<<4) + (mvx/2) + offset > (mb_width<<4) - bsize) {
              if (!quiet)
        printf("mvx out of range: searching for sync\n");
              fault = 1;
            }
            offset = k ? (((k-1)&2)<<2) : 0;
            if ((ypos<<4) + (mvy/2) + offset < 0 ||
        (ypos<<4) + (mvy/2) + offset > (mb_height<<4) - bsize) {
              if (!quiet)
        printf("mvy out of range: searching for sync\n");
              fault = 1;
            }
          }
          MV[0][k][ypos+1][xpos+1] = mvx;
          MV[1][k][ypos+1][xpos+1] = mvy;
        }

        /* PB frame delta vectors */

        if (pb_frame) {
          if (MODB == PBMODE_MVDB || MODB == PBMODE_CBPB_MVDB) {
            if (syntax_arith_coding) {
              mvdbx_index = decode_a_symbol(cumf_MVD);
              mvdbx = mvdtab[mvdbx_index];
              
              mvdby_index = decode_a_symbol(cumf_MVD);
              mvdby = mvdtab[mvdby_index];
            }
            else {
              mvdbx = getTMNMV();
              mvdby = getTMNMV();
            }


            mvdbx = motion_decode(mvdbx, 0);
            mvdby = motion_decode(mvdby, 0);
            /* This will not work if the PB deltas are so large they
               require the second colums of the motion vector VLC
               table to be used.  To fix this it is necessary to
               calculate the MV predictor for the PB delta: TRB*MV/TRD
               here, and use this as the second parameter to
               motion_decode(). The B vector itself will then be
               returned from motion_decode(). This will have to be
               changed to the PB delta again, since it is the PB delta
               which is used later in this program. I don't think PB
               deltas outside the range mentioned above is useful, but
               you never know... */

            if (trace) {
              printf("MVDB x: %d\n", mvdbx);
              printf("MVDB y: %d\n", mvdby);
            }
          }
          else {
            mvdbx = 0; 
            mvdby = 0;
          }
        }
      }

      if (fault) goto resync;

    }
    else { /* COD == 1 --> skipped MB */
      if (MBA>=MBAmax)
        return; /* all macroblocks decoded */
      if (!syntax_arith_coding)
        if (pict_type == PCT_INTER)
          flushbits(1);

      Mode = MODE_INTER;
      
      /* Reset CBP */
      CBP = CBPB = 0;

      /* reset motion vectors */
      MV[0][0][ypos+1][xpos+1] = 0;
      MV[1][0][ypos+1][xpos+1] = 0;
      mvdbx = 0;
      mvdby = 0;
    }

    /* Store Mode*/
    modemap[ypos+1][xpos+1] = Mode;

    if (Mode == MODE_INTRA || Mode == MODE_INTRA_Q) 
      if (!pb_frame)
        MV[0][0][ypos+1][xpos+1]=MV[1][0][ypos+1][xpos+1] = 0;


  reconstruct_mb:

    /* pixel coordinates of top left corner of current macroblock */
    /* one delayed because of OBMC */
    if (xpos > 0) {
      bx = 16*(xpos-1);
      by = 16*ypos;
    }
    else {
      bx = coded_picture_width-16;
      by = 16*(ypos-1);
    }

    if (MBA > 0) {

      Mode = modemap[by/16+1][bx/16+1];

      /* forward motion compensation for B-frame */
      if (pb_frame)
        reconstruct(bx,by,0,pmvdbx,pmvdby);
      
      /* motion compensation for P-frame */
      if (Mode == MODE_INTER || Mode == MODE_INTER_Q || Mode == MODE_INTER4V)
        reconstruct(bx,by,1,0,0);

      /* copy or add block data into P-picture */
      for (comp=0; comp<blk_cnt; comp++) {
        /* inverse DCT */
        if (Mode == MODE_INTRA || Mode == MODE_INTRA_Q) {
          if (refidct)
            idctref(ld->block[comp]);//此函数执行IDCT变换
          else
            idct(ld->block[comp]);
          addblock(comp,bx,by,0);
        }
        else if ( (pCBP & (1<<(blk_cnt-1-comp))) ) {
          /* No need to to do this for blocks with no coeffs */
          if (refidct)
            idctref(ld->block[comp]);
          else
            idct(ld->block[comp]);
          addblock(comp,bx,by,1);
        }
      }
      
      
      if (pb_frame) {
        /* add block data into B-picture */
        for (comp = 6; comp<blk_cnt+6; comp++) {
          if (!pCOD || adv_pred_mode)
            reconblock_b(comp-6,bx,by,Mode,pmvdbx,pmvdby);
          if ( (pCBPB & (1<<(blk_cnt-1-comp%6))) ) {
            if (refidct)
              idctref(ld->block[comp]);
            else
              idct(ld->block[comp]);
            addblock(comp,bx,by,1);
          }
        }
      }
      
    } /* end if (MBA > 0) */

    if (!COD) {

      Mode = modemap[ypos+1][xpos+1];

      /* decode blocks */
      for (comp=0; comp<blk_cnt; comp++) {

        clearblock(comp);
        if (Mode == MODE_INTRA || Mode == MODE_INTRA_Q) { /* Intra */
          bp = ld->block[comp];
          if(syntax_arith_coding) {
            INTRADC_index = decode_a_symbol(cumf_INTRADC);
            bp[0] = intradctab[INTRADC_index];
            if (trace)
              printf("INTRADC Index: %d INTRADC: %d \n", INTRADC_index, bp[0]);
          }
          else {
            bp[0] = getbits(8);
            if (trace) {
              printf("DC[%d]: (",comp);
              printbits((int)bp[0],8,8);
              printf("): %d\n",(int)bp[0]);
            }
          }

          if (bp[0] == 128)
            if (!quiet)
              fprintf(stderr,"Illegal DC-coeff: 1000000\n");
          if (bp[0] == 255)  /* Spec. in H.26P, not in TMN4 */
            bp[0] = 128;
          bp[0] *= 8; /* Iquant */
          if ( (CBP & (1<<(blk_cnt-1-comp))) ) {
            if (!syntax_arith_coding)
              getblock(comp,0);
            else 
              get_sac_block(comp,0);
          }
        }
        else { /* Inter */
          if ( (CBP & (1<<(blk_cnt-1-comp))) ) {
            if (!syntax_arith_coding)
              getblock(comp,1);
            else
              get_sac_block(comp,1);
          }

        }
        if (fault) goto resync;
      }

      /* Decode B blocks */
      if (pb_frame) {
        for (comp=6; comp<blk_cnt+6; comp++) {
          clearblock(comp);
          if ( (CBPB & (1<<(blk_cnt-1-comp%6))) ) {
            if (!syntax_arith_coding)
              getblock(comp,1);
            else
              get_sac_block(comp,1);
          }
          if (fault) goto resync;
        }
      }
          
    }

    /* advance to next macroblock */
    MBA++;

    pCBP = CBP; pCBPB = CBPB; pCOD = COD;
    pmvdbx = mvdbx; pmvdby = mvdby;
    fflush(stdout);

    if (MBA >= MBAmax && !last_done) {
      COD = 1;
      xpos = 0;
      ypos++;
      last_done = 1;
      goto reconstruct_mb;
    }

  }
}

/* set block to zero */

static void clearblock(comp)
int comp;
{
  int *bp;
  int i;

  bp = (int *)ld->block[comp];

  for (i=0; i<8; i++)
  {
    bp[0] = bp[1] = bp[2] = bp[3] = 0;
    bp += 4;
  }
}


/* move/add 8x8-Block from block[comp] to refframe or bframe */

static void addblock(comp,bx,by,addflag)
int comp,bx,by,addflag;
{
  int cc,i, iincr, P = 1;
  unsigned char *rfp;
  short *bp;

  bp = ld->block[comp];

  if (comp >= 6) {
    /* This is a component for B-frame forward prediction */
    P = 0;
    addflag = 1;
    comp -= 6;
  }

  cc = (comp<4) ? 0 : (comp&1)+1; /* color component index */

  if (cc==0) {
    /* luminance */
    
    /* frame DCT coding */
    if (P)
      rfp = newframe[0]
        + coded_picture_width*(by+((comp&2)<<2)) + bx + ((comp&1)<<3);
    else
      rfp = bframe[0]
        + coded_picture_width*(by+((comp&2)<<2)) + bx + ((comp&1)<<3);
    iincr = coded_picture_width;
  }
  else {
    /* chrominance */

    /* scale coordinates */
    bx >>= 1;
    by >>= 1;
    /* frame DCT coding */
    if (P)
      rfp = newframe[cc] + chrom_width*by + bx;
    else
      rfp = bframe[cc] + chrom_width*by + bx;
    iincr = chrom_width;
  }


  if (addflag) {
    for (i=0; i<8; i++) {
      rfp[0] = clp[bp[0]+rfp[0]];
      rfp[1] = clp[bp[1]+rfp[1]];
      rfp[2] = clp[bp[2]+rfp[2]];
      rfp[3] = clp[bp[3]+rfp[3]];
      rfp[4] = clp[bp[4]+rfp[4]];
      rfp[5] = clp[bp[5]+rfp[5]];
      rfp[6] = clp[bp[6]+rfp[6]];
      rfp[7] = clp[bp[7]+rfp[7]];
      bp += 8;
      rfp+= iincr;
    }
  }