getpic.c

MPEG2视频编解码算法方面的源代码(包括编码和解码)

  *pdct_type = dct_type;
}


/* move/add 8x8-Block from block[comp] to backward_reference_frame */
/* copy reconstructed 8x8 block from block[comp] to current_frame[]
 * ISO/IEC 13818-2 section 7.6.8: Adding prediction and coefficient data
 * This stage also embodies some of the operations implied by:
 *   - ISO/IEC 13818-2 section 7.6.7: Combining predictions
 *   - ISO/IEC 13818-2 section 6.1.3: Macroblock
*/
static void Add_Block(comp,bx,by,dct_type,addflag)
int comp,bx,by,dct_type,addflag;
{
  int cc,i, j, iincr;
  unsigned char *rfp;
  short *bp;

  
  /* derive color component index */
  /* equivalent to ISO/IEC 13818-2 Table 7-1 */
  cc = (comp<4) ? 0 : (comp&1)+1; /* color component index */

  if (cc==0)
  {
    /* luminance */

    if (picture_structure==FRAME_PICTURE)
      if (dct_type)
      {
        /* field DCT coding */
        rfp = current_frame[0]
              + Coded_Picture_Width*(by+((comp&2)>>1)) + bx + ((comp&1)<<3);
        iincr = (Coded_Picture_Width<<1) - 8;
      }
      else
      {
        /* frame DCT coding */
        rfp = current_frame[0]
              + Coded_Picture_Width*(by+((comp&2)<<2)) + bx + ((comp&1)<<3);
        iincr = Coded_Picture_Width - 8;
      }
    else
    {
      /* field picture */
      rfp = current_frame[0]
            + (Coded_Picture_Width<<1)*(by+((comp&2)<<2)) + bx + ((comp&1)<<3);
      iincr = (Coded_Picture_Width<<1) - 8;
    }
  }
  else
  {
    /* chrominance */

    /* scale coordinates */
    if (chroma_format!=CHROMA444)
      bx >>= 1;
    if (chroma_format==CHROMA420)
      by >>= 1;
    if (picture_structure==FRAME_PICTURE)
    {
      if (dct_type && (chroma_format!=CHROMA420))
      {
        /* field DCT coding */
        rfp = current_frame[cc]
              + Chroma_Width*(by+((comp&2)>>1)) + bx + (comp&8);
        iincr = (Chroma_Width<<1) - 8;
      }
      else
      {
        /* frame DCT coding */
        rfp = current_frame[cc]
              + Chroma_Width*(by+((comp&2)<<2)) + bx + (comp&8);
        iincr = Chroma_Width - 8;
      }
    }
    else
    {
      /* field picture */
      rfp = current_frame[cc]
            + (Chroma_Width<<1)*(by+((comp&2)<<2)) + bx + (comp&8);
      iincr = (Chroma_Width<<1) - 8;
    }
  }

  bp = ld->block[comp];

  if (addflag)
  {
    for (i=0; i<8; i++)
    {
      for (j=0; j<8; j++)
      {
        *rfp = Clip[*bp++ + *rfp];
        rfp++;
      }

      rfp+= iincr;
    }
  }
  else
  {
    for (i=0; i<8; i++)
    {
      for (j=0; j<8; j++)
        *rfp++ = Clip[*bp++ + 128];

      rfp+= iincr;
    }
  }
}


/* ISO/IEC 13818-2 section 7.8 */
static void Decode_SNR_Macroblock(SNRMBA, SNRMBAinc, MBA, MBAmax, dct_type)
  int *SNRMBA, *SNRMBAinc;
  int MBA, MBAmax;
  int *dct_type;
{
  int SNRmacroblock_type, SNRcoded_block_pattern, SNRdct_type, dummy; 
  int slice_vert_pos_ext, quantizer_scale_code, comp, code;

  ld = &enhan;

  if (*SNRMBAinc==0)
  {
    if (!Show_Bits(23)) /* next_start_code */
    {
      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("SNR: Premature end of picture\n");
        return;
      }

      Flush_Buffer32();

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

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

      /* set current location */
      *SNRMBA =
        ((slice_vert_pos_ext<<7) + (code&255) - 1)*mb_width + *SNRMBAinc - 1;

      *SNRMBAinc = 1; /* first macroblock in slice: not skipped */
    }
    else /* not next_start_code */
    {
      if (*SNRMBA>=MBAmax)
      {
        if (!Quiet_Flag)
          printf("Too many macroblocks in picture\n");
        return;
      }

      /* decode macroblock address increment */
      *SNRMBAinc = Get_macroblock_address_increment();
    }
  }

  if (*SNRMBA!=MBA)
  {
    /* streams out of sync */
    if (!Quiet_Flag)
      printf("Cant't synchronize streams\n");
    return;
  }

  if (*SNRMBAinc==1) /* not skipped */
  {
    macroblock_modes(&SNRmacroblock_type, &dummy, &dummy,
      &dummy, &dummy, &dummy, &dummy, &dummy,
      &SNRdct_type);

    if (SNRmacroblock_type & MACROBLOCK_PATTERN)
      *dct_type = SNRdct_type;

    if (SNRmacroblock_type & MACROBLOCK_QUANT)
    {
      quantizer_scale_code = Get_Bits(5);
      ld->quantizer_scale =
        ld->q_scale_type ? Non_Linear_quantizer_scale[quantizer_scale_code] : quantizer_scale_code<<1;
    }

    /* macroblock_pattern */
    if (SNRmacroblock_type & MACROBLOCK_PATTERN)
    {
      SNRcoded_block_pattern = Get_coded_block_pattern();

      if (chroma_format==CHROMA422)
        SNRcoded_block_pattern = (SNRcoded_block_pattern<<2) | Get_Bits(2); /* coded_block_pattern_1 */
      else if (chroma_format==CHROMA444)
        SNRcoded_block_pattern = (SNRcoded_block_pattern<<6) | Get_Bits(6); /* coded_block_pattern_2 */
    }
    else
      SNRcoded_block_pattern = 0;

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

      if (SNRcoded_block_pattern & (1<<(block_count-1-comp)))
        Decode_MPEG2_Non_Intra_Block(comp);
    }
  }
  else /* SNRMBAinc!=1: skipped macroblock */
  {
    for (comp=0; comp<block_count; comp++)
      Clear_Block(comp);
  }

  ld = &base;
}



/* IMPLEMENTATION: set scratch pad macroblock to zero */
static void Clear_Block(comp)
int comp;
{
  short *Block_Ptr;
  int i;

  Block_Ptr = ld->block[comp];

  for (i=0; i<64; i++)
    *Block_Ptr++ = 0;
}


/* SCALABILITY: add SNR enhancement layer block data to base layer */
/* ISO/IEC 13818-2 section 7.8.3.4: Addition of coefficients from the two layes */
static void Sum_Block(comp)
int comp;
{
  short *Block_Ptr1, *Block_Ptr2;
  int i;

  Block_Ptr1 = base.block[comp];
  Block_Ptr2 = enhan.block[comp];

  for (i=0; i<64; i++)
    *Block_Ptr1++ += *Block_Ptr2++;
}


/* limit coefficients to -2048..2047 */
/* ISO/IEC 13818-2 section 7.4.3 and 7.4.4: Saturation and Mismatch control */
static void Saturate(Block_Ptr)
short *Block_Ptr;
{
  int i, sum, val;

  sum = 0;

  /* ISO/IEC 13818-2 section 7.4.3: Saturation */
  for (i=0; i<64; i++)
  {
    val = Block_Ptr[i];

    if (val>2047)
      val = 2047;
    else if (val<-2048)
      val = -2048;

    Block_Ptr[i] = val;
    sum+= val;
  }

  /* ISO/IEC 13818-2 section 7.4.4: Mismatch control */
  if ((sum&1)==0)
    Block_Ptr[63]^= 1;

}


/* reuse old picture buffers as soon as they are no longer needed 
   based on life-time axioms of MPEG */
static void Update_Picture_Buffers()
{                           
  int cc;              /* color component index */
  unsigned char *tmp;  /* temporary swap pointer */

  for (cc=0; cc<3; cc++)
  {
    /* B pictures do not need to be save for future reference */
    if (picture_coding_type==B_TYPE)
    {
      current_frame[cc] = auxframe[cc];
    }
    else
    {
      /* only update at the beginning of the coded frame */
      if (!Second_Field)
      {
        tmp = forward_reference_frame[cc];

        /* the previously decoded reference frame is stored
           coincident with the location where the backward 
           reference frame is stored (backwards prediction is not
           needed in P pictures) */
        forward_reference_frame[cc] = backward_reference_frame[cc];
        
        /* update pointer for potential future B pictures */
        backward_reference_frame[cc] = tmp;
      }

      /* can erase over old backward reference frame since it is not used
         in a P picture, and since any subsequent B pictures will use the 
         previously decoded I or P frame as the backward_reference_frame */
      current_frame[cc] = backward_reference_frame[cc];
    }

    /* IMPLEMENTATION:
       one-time folding of a line offset into the pointer which stores the
       memory address of the current frame saves offsets and conditional 
       branches throughout the remainder of the picture processing loop */
    if (picture_structure==BOTTOM_FIELD)
      current_frame[cc]+= (cc==0) ? Coded_Picture_Width : Chroma_Width;
  }
}


/* store last frame */

void Output_Last_Frame_of_Sequence(Framenum)
int Framenum;
{
  if (Second_Field)
    printf("last frame incomplete, not stored\n");
  else
    Write_Frame(backward_reference_frame,Framenum-1);
}



static void frame_reorder(Bitstream_Framenum, Sequence_Framenum)
int Bitstream_Framenum, Sequence_Framenum;
{
  /* tracking variables to insure proper output in spatial scalability */
  static int Oldref_progressive_frame, Newref_progressive_frame;

  if (Sequence_Framenum!=0)
  {
    if (picture_structure==FRAME_PICTURE || Second_Field)
    {
      if (picture_coding_type==B_TYPE)
        Write_Frame(auxframe,Bitstream_Framenum-1);
      else
      {
        Newref_progressive_frame = progressive_frame;
        progressive_frame = Oldref_progressive_frame;

        Write_Frame(forward_reference_frame,Bitstream_Framenum-1);

        Oldref_progressive_frame = progressive_frame = Newref_progressive_frame;
      }
    }
#ifdef DISPLAY
    else if (Output_Type==T_X11)
    {
      if(!Display_Progressive_Flag)
        Display_Second_Field();
    }
#endif
  }
  else
    Oldref_progressive_frame = progressive_frame;

}


/* ISO/IEC 13818-2 section 7.6 */
static void motion_compensation(MBA, macroblock_type, motion_type, PMV, 
  motion_vertical_field_select, dmvector, stwtype, dct_type)
int MBA;
int macroblock_type;
int motion_type;
int PMV[2][2][2];
int motion_vertical_field_select[2][2];
int dmvector[2];
int stwtype;
int dct_type;
{
  int bx, by;
  int comp;

  /* derive current macroblock position within picture */
  /* ISO/IEC 13818-2 section 6.3.1.6 and 6.3.1.7 */
  bx = 16*(MBA%mb_width);
  by = 16*(MBA/mb_width);

  /* motion compensation */
  if (!(macroblock_type & MACROBLOCK_INTRA))
    form_predictions(bx,by,macroblock_type,motion_type,PMV,
      motion_vertical_field_select,dmvector,stwtype);
  
  /* SCALABILITY: Data Partitioning */
  if (base.scalable_mode==SC_DP)
    ld = &base;