getpic.c

MPEG2视频编解码算法方面的源代码(包括编码和解码)

  /* copy or add block data into picture */
  for (comp=0; comp<block_count; comp++)
  {
    /* SCALABILITY: SNR */
    /* ISO/IEC 13818-2 section 7.8.3.4: Addition of coefficients from 
       the two a layers */
    if (Two_Streams && enhan.scalable_mode==SC_SNR)
      Sum_Block(comp); /* add SNR enhancement layer data to base layer */

    /* MPEG-2 saturation and mismatch control */
    /* base layer could be MPEG-1 stream, enhancement MPEG-2 SNR */
    /* ISO/IEC 13818-2 section 7.4.3 and 7.4.4: Saturation and Mismatch control */
    if ((Two_Streams && enhan.scalable_mode==SC_SNR) || ld->MPEG2_Flag)
      Saturate(ld->block[comp]);

    /* ISO/IEC 13818-2 section Annex A: inverse DCT */
    if (Reference_IDCT_Flag)
      Reference_IDCT(ld->block[comp]);
    else
      Fast_IDCT(ld->block[comp]);
    
    /* ISO/IEC 13818-2 section 7.6.8: Adding prediction and coefficient data */
    Add_Block(comp,bx,by,dct_type,(macroblock_type & MACROBLOCK_INTRA)==0);
  }

}



/* ISO/IEC 13818-2 section 7.6.6 */
static void skipped_macroblock(dc_dct_pred, PMV, motion_type, 
  motion_vertical_field_select, stwtype, macroblock_type)
int dc_dct_pred[3];
int PMV[2][2][2];
int *motion_type;
int motion_vertical_field_select[2][2];
int *stwtype;
int *macroblock_type;
{
  int comp;
  
  /* SCALABILITY: Data Paritioning */
  if (base.scalable_mode==SC_DP)
    ld = &base;

  for (comp=0; comp<block_count; comp++)
    Clear_Block(comp);

  /* reset intra_dc predictors */
  /* ISO/IEC 13818-2 section 7.2.1: DC coefficients in intra blocks */
  dc_dct_pred[0]=dc_dct_pred[1]=dc_dct_pred[2]=0;

  /* reset motion vector predictors */
  /* ISO/IEC 13818-2 section 7.6.3.4: Resetting motion vector predictors */
  if (picture_coding_type==P_TYPE)
    PMV[0][0][0]=PMV[0][0][1]=PMV[1][0][0]=PMV[1][0][1]=0;

  /* derive motion_type */
  if (picture_structure==FRAME_PICTURE)
    *motion_type = MC_FRAME;
  else
  {
    *motion_type = MC_FIELD;

    /* predict from field of same parity */
    /* ISO/IEC 13818-2 section 7.6.6.1 and 7.6.6.3: P field picture and B field
       picture */
    motion_vertical_field_select[0][0]=motion_vertical_field_select[0][1] = 
      (picture_structure==BOTTOM_FIELD);
  }

  /* skipped I are spatial-only predicted, */
  /* skipped P and B are temporal-only predicted */
  /* ISO/IEC 13818-2 section 7.7.6: Skipped macroblocks */
  *stwtype = (picture_coding_type==I_TYPE) ? 8 : 0;

 /* IMPLEMENTATION: clear MACROBLOCK_INTRA */
  *macroblock_type&= ~MACROBLOCK_INTRA;

}


/* return==-1 means go to next picture */
/* the expression "start of slice" is used throughout the normative
   body of the MPEG specification */
static int start_of_slice(MBAmax, MBA, MBAinc, 
  dc_dct_pred, PMV)
int MBAmax;
int *MBA;
int *MBAinc;
int dc_dct_pred[3];
int PMV[2][2][2];
{
  unsigned int code;
  int slice_vert_pos_ext;

  ld = &base;

  Fault_Flag = 0;

  next_start_code();
  code = Show_Bits(32);

  if (code<SLICE_START_CODE_MIN || code>SLICE_START_CODE_MAX)
  {
    /* only slice headers are allowed in picture_data */
    if (!Quiet_Flag)
      printf("start_of_slice(): Premature end of picture\n");

    return(-1);  /* trigger: go to next picture */
  }

  Flush_Buffer32(); 

  /* decode slice header (may change quantizer_scale) */
  slice_vert_pos_ext = slice_header();

 
  /* SCALABILITY: Data Partitioning */
  if (base.scalable_mode==SC_DP)
  {
    ld = &enhan;
    next_start_code();
    code = Show_Bits(32);

    if (code<SLICE_START_CODE_MIN || code>SLICE_START_CODE_MAX)
    {
      /* only slice headers are allowed in picture_data */
      if (!Quiet_Flag)
        printf("DP: Premature end of picture\n");
      return(-1);    /* trigger: go to next picture */
    }

    Flush_Buffer32();

    /* decode slice header (may change quantizer_scale) */
    slice_vert_pos_ext = slice_header();

    if (base.priority_breakpoint!=1)
      ld = &base;
  }

  /* decode macroblock address increment */
  *MBAinc = Get_macroblock_address_increment();

  if (Fault_Flag) 
  {
    printf("start_of_slice(): MBAinc unsuccessful\n");
    return(0);   /* trigger: go to next slice */
  }

  /* set current location */
  /* NOTE: the arithmetic used to derive macroblock_address below is
   *       equivalent to ISO/IEC 13818-2 section 6.3.17: Macroblock
   */
  *MBA = ((slice_vert_pos_ext<<7) + (code&255) - 1)*mb_width + *MBAinc - 1;
  *MBAinc = 1; /* first macroblock in slice: not skipped */

  /* reset all DC coefficient and motion vector predictors */
  /* reset all DC coefficient and motion vector predictors */
  /* ISO/IEC 13818-2 section 7.2.1: DC coefficients in intra blocks */
  dc_dct_pred[0]=dc_dct_pred[1]=dc_dct_pred[2]=0;
  
  /* ISO/IEC 13818-2 section 7.6.3.4: Resetting motion vector predictors */
  PMV[0][0][0]=PMV[0][0][1]=PMV[1][0][0]=PMV[1][0][1]=0;
  PMV[0][1][0]=PMV[0][1][1]=PMV[1][1][0]=PMV[1][1][1]=0;

  /* successfull: trigger decode macroblocks in slice */
  return(1);
}


/* ISO/IEC 13818-2 sections 7.2 through 7.5 */
static int decode_macroblock(macroblock_type, stwtype, stwclass,
  motion_type, dct_type, PMV, dc_dct_pred, 
  motion_vertical_field_select, dmvector)
int *macroblock_type; 
int *stwtype;
int *stwclass;
int *motion_type; 
int *dct_type;
int PMV[2][2][2]; 
int dc_dct_pred[3]; 
int motion_vertical_field_select[2][2];
int dmvector[2];
{
  /* locals */
  int quantizer_scale_code; 
  int comp;

  int motion_vector_count; 
  int mv_format; 
  int dmv; 
  int mvscale;
  int coded_block_pattern;

  /* SCALABILITY: Data Patitioning */
  if (base.scalable_mode==SC_DP)
  {
    if (base.priority_breakpoint<=2)
      ld = &enhan;
    else
      ld = &base;
  }

  /* ISO/IEC 13818-2 section 6.3.17.1: Macroblock modes */
  macroblock_modes(macroblock_type, stwtype, stwclass,
    motion_type, &motion_vector_count, &mv_format, &dmv, &mvscale,
    dct_type);

  if (Fault_Flag) return(0);  /* trigger: go to next slice */

  if (*macroblock_type & MACROBLOCK_QUANT)
  {
    quantizer_scale_code = Get_Bits(5);

#ifdef TRACE
    if (Trace_Flag)
    {
      printf("quantiser_scale_code (");
      Print_Bits(quantizer_scale_code,5,5);
      printf("): %d\n",quantizer_scale_code);
    }
#endif /* TRACE */

    /* ISO/IEC 13818-2 section 7.4.2.2: Quantizer scale factor */
    if (ld->MPEG2_Flag)
      ld->quantizer_scale =
      ld->q_scale_type ? Non_Linear_quantizer_scale[quantizer_scale_code] 
       : (quantizer_scale_code << 1);
    else
      ld->quantizer_scale = quantizer_scale_code;

    /* SCALABILITY: Data Partitioning */
    if (base.scalable_mode==SC_DP)
      /* make sure base.quantizer_scale is valid */
      base.quantizer_scale = ld->quantizer_scale;
  }

  /* motion vectors */


  /* ISO/IEC 13818-2 section 6.3.17.2: Motion vectors */

  /* decode forward motion vectors */
  if ((*macroblock_type & MACROBLOCK_MOTION_FORWARD) 
    || ((*macroblock_type & MACROBLOCK_INTRA) 
    && concealment_motion_vectors))
  {
    if (ld->MPEG2_Flag)
      motion_vectors(PMV,dmvector,motion_vertical_field_select,
        0,motion_vector_count,mv_format,f_code[0][0]-1,f_code[0][1]-1,
        dmv,mvscale);
    else
      motion_vector(PMV[0][0],dmvector,
      forward_f_code-1,forward_f_code-1,0,0,full_pel_forward_vector);
  }

  if (Fault_Flag) return(0);  /* trigger: go to next slice */

  /* decode backward motion vectors */
  if (*macroblock_type & MACROBLOCK_MOTION_BACKWARD)
  {
    if (ld->MPEG2_Flag)
      motion_vectors(PMV,dmvector,motion_vertical_field_select,
        1,motion_vector_count,mv_format,f_code[1][0]-1,f_code[1][1]-1,0,
        mvscale);
    else
      motion_vector(PMV[0][1],dmvector,
        backward_f_code-1,backward_f_code-1,0,0,full_pel_backward_vector);
  }

  if (Fault_Flag) return(0);  /* trigger: go to next slice */

  if ((*macroblock_type & MACROBLOCK_INTRA) && concealment_motion_vectors)
    Flush_Buffer(1); /* remove marker_bit */

  if (base.scalable_mode==SC_DP && base.priority_breakpoint==3)
    ld = &enhan;

  /* macroblock_pattern */
  /* ISO/IEC 13818-2 section 6.3.17.4: Coded block pattern */
  if (*macroblock_type & MACROBLOCK_PATTERN)
  {
    coded_block_pattern = Get_coded_block_pattern();

    if (chroma_format==CHROMA422)
    {
      /* coded_block_pattern_1 */
      coded_block_pattern = (coded_block_pattern<<2) | Get_Bits(2); 

#ifdef TRACE
       if (Trace_Flag)
       {
         printf("coded_block_pattern_1: ");
         Print_Bits(coded_block_pattern,2,2);
         printf(" (%d)\n",coded_block_pattern&3);
       }
#endif /* TRACE */
     }
     else if (chroma_format==CHROMA444)
     {
      /* coded_block_pattern_2 */
      coded_block_pattern = (coded_block_pattern<<6) | Get_Bits(6); 

#ifdef TRACE
      if (Trace_Flag)
      {
        printf("coded_block_pattern_2: ");
        Print_Bits(coded_block_pattern,6,6);
        printf(" (%d)\n",coded_block_pattern&63);
      }
#endif /* TRACE */
    }
  }
  else
    coded_block_pattern = (*macroblock_type & MACROBLOCK_INTRA) ? 
      (1<<block_count)-1 : 0;

  if (Fault_Flag) return(0);  /* trigger: go to next slice */

  /* decode blocks */
  for (comp=0; comp<block_count; comp++)
  {
    /* SCALABILITY: Data Partitioning */
    if (base.scalable_mode==SC_DP)
    ld = &base;

    Clear_Block(comp);

    if (coded_block_pattern & (1<<(block_count-1-comp)))
    {
      if (*macroblock_type & MACROBLOCK_INTRA)
      {
        if (ld->MPEG2_Flag)
          Decode_MPEG2_Intra_Block(comp,dc_dct_pred);
        else
          Decode_MPEG1_Intra_Block(comp,dc_dct_pred);
      }
      else
      {
        if (ld->MPEG2_Flag)
          Decode_MPEG2_Non_Intra_Block(comp);
        else
          Decode_MPEG1_Non_Intra_Block(comp);
      }

      if (Fault_Flag) return(0);  /* trigger: go to next slice */
    }
  }

  if(picture_coding_type==D_TYPE)
  {
    /* remove end_of_macroblock (always 1, prevents startcode emulation) */
    /* ISO/IEC 11172-2 section 2.4.2.7 and 2.4.3.6 */
    marker_bit("D picture end_of_macroblock bit");
  }

  /* reset intra_dc predictors */
  /* ISO/IEC 13818-2 section 7.2.1: DC coefficients in intra blocks */
  if (!(*macroblock_type & MACROBLOCK_INTRA))
    dc_dct_pred[0]=dc_dct_pred[1]=dc_dct_pred[2]=0;

  /* reset motion vector predictors */
  if ((*macroblock_type & MACROBLOCK_INTRA) && !concealment_motion_vectors)
  {
    /* intra mb without concealment motion vectors */
    /* ISO/IEC 13818-2 section 7.6.3.4: Resetting motion vector predictors */
    PMV[0][0][0]=PMV[0][0][1]=PMV[1][0][0]=PMV[1][0][1]=0;
    PMV[0][1][0]=PMV[0][1][1]=PMV[1][1][0]=PMV[1][1][1]=0;
  }

  /* special "No_MC" macroblock_type case */
  /* ISO/IEC 13818-2 section 7.6.3.5: Prediction in P pictures */
  if ((picture_coding_type==P_TYPE) 
    && !(*macroblock_type & (MACROBLOCK_MOTION_FORWARD|MACROBLOCK_INTRA)))
  {
    /* non-intra mb without forward mv in a P picture */
    /* ISO/IEC 13818-2 section 7.6.3.4: Resetting motion vector predictors */
    PMV[0][0][0]=PMV[0][0][1]=PMV[1][0][0]=PMV[1][0][1]=0;

    /* derive motion_type */
    /* ISO/IEC 13818-2 section 6.3.17.1: Macroblock modes, frame_motion_type */
    if (picture_structure==FRAME_PICTURE)
      *motion_type = MC_FRAME;
    else
    {
      *motion_type = MC_FIELD;
      /* predict from field of same parity */
      motion_vertical_field_select[0][0] = (picture_structure==BOTTOM_FIELD);
    }
  }

  if (*stwclass==4)
  {
    /* purely spatially predicted macroblock */
    /* ISO/IEC 13818-2 section 7.7.5.1: Resetting motion vector predictions */
    PMV[0][0][0]=PMV[0][0][1]=PMV[1][0][0]=PMV[1][0][1]=0;
    PMV[0][1][0]=PMV[0][1][1]=PMV[1][1][0]=PMV[1][1][1]=0;
  }

  /* successfully decoded macroblock */
  return(1);

} /* decode_macroblock */