getpic.c

MPEG2解编码程序源代码

/* getpic.c, picture decoding                                               */

/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */

/*
 * Disclaimer of Warranty
 *
 * These software programs are available to the user without any license fee or
 * royalty on an "as is" basis.  The MPEG Software Simulation Group disclaims
 * any and all warranties, whether express, implied, or statuary, including any
 * implied warranties or merchantability or of fitness for a particular
 * purpose.  In no event shall the copyright-holder be liable for any
 * incidental, punitive, or consequential damages of any kind whatsoever
 * arising from the use of these programs.
 *
 * This disclaimer of warranty extends to the user of these programs and user's
 * customers, employees, agents, transferees, successors, and assigns.
 *
 * The MPEG Software Simulation Group does not represent or warrant that the
 * programs furnished hereunder are free of infringement of any third-party
 * patents.
 *
 * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
 * are subject to royalty fees to patent holders.  Many of these patents are
 * general enough such that they are unavoidable regardless of implementation
 * design.
 *
 */

#include <stdio.h>

#include "config.h"
#include "global.h"

/* private prototypes*/
static void picture_data _ANSI_ARGS_((int framenum));
static void macroblock_modes _ANSI_ARGS_((int *pmacroblock_type, int *pstwtype,
  int *pstwclass, int *pmotion_type, int *pmotion_vector_count, int *pmv_format, int *pdmv,
  int *pmvscale, int *pdct_type));
static void Clear_Block _ANSI_ARGS_((int comp));
static void Sum_Block _ANSI_ARGS_((int comp));
static void Saturate _ANSI_ARGS_((short *bp));
static void Add_Block _ANSI_ARGS_((int comp, int bx, int by,
  int dct_type, int addflag));
static void Update_Picture_Buffers _ANSI_ARGS_((void));
static void frame_reorder _ANSI_ARGS_((int bitstream_framenum, 
  int sequence_framenum));
static void Decode_SNR_Macroblock _ANSI_ARGS_((int *SNRMBA, int *SNRMBAinc, 
  int MBA, int MBAmax, int *dct_type));

static void motion_compensation _ANSI_ARGS_((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));

static void skipped_macroblock _ANSI_ARGS_((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));

static int slice _ANSI_ARGS_((int framenum, int MBAmax));

static int start_of_slice _ANSI_ARGS_ ((int MBAmax, int *MBA,
  int *MBAinc, int dc_dct_pred[3], int PMV[2][2][2]));

static int decode_macroblock _ANSI_ARGS_((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]));


/* decode one frame or field picture */
void Decode_Picture(bitstream_framenum, sequence_framenum)
int bitstream_framenum, sequence_framenum;
{

  if (picture_structure==FRAME_PICTURE && Second_Field)
  {
    /* recover from illegal number of field pictures */
    printf("odd number of field pictures\n");
    Second_Field = 0;
  }

  /* IMPLEMENTATION: update picture buffer pointers */
  Update_Picture_Buffers();

#ifdef VERIFY 
  Check_Headers(bitstream_framenum, sequence_framenum);
#endif /* VERIFY */

  /* ISO/IEC 13818-4 section 2.4.5.4 "frame buffer intercept method" */
  /* (section number based on November 1995 (Dallas) draft of the 
      conformance document) */
  if(Ersatz_Flag)
    Substitute_Frame_Buffer(bitstream_framenum, sequence_framenum);

  /* form spatial scalable picture */
 
  /* form spatial scalable picture */
  /* ISO/IEC 13818-2 section 7.7: Spatial scalability */
  if (base.pict_scal && !Second_Field) 
  {
    Spatial_Prediction();
  }

  /* decode picture data ISO/IEC 13818-2 section 6.2.3.7 */
  picture_data(bitstream_framenum);

  /* write or display current or previously decoded reference frame */
  /* ISO/IEC 13818-2 section 6.1.1.11: Frame reordering */
  frame_reorder(bitstream_framenum, sequence_framenum);

  if (picture_structure!=FRAME_PICTURE)
    Second_Field = !Second_Field;
}


/* decode all macroblocks of the current picture */
/* stages described in ISO/IEC 13818-2 section 7 */
static void picture_data(framenum)
int framenum;
{
  int MBAmax;
  int ret;

  /* number of macroblocks per picture */
  MBAmax = mb_width*mb_height;

  if (picture_structure!=FRAME_PICTURE)
    MBAmax>>=1; /* field picture has half as mnay macroblocks as frame */

  for(;;)
  {
    if((ret=slice(framenum, MBAmax))<0)
      return;
  }

}



/* decode all macroblocks of the current picture */
/* ISO/IEC 13818-2 section 6.3.16 */
static int slice(framenum, MBAmax)
int framenum, MBAmax;
{
  int MBA; 
  int MBAinc, macroblock_type, motion_type, dct_type;
  int dc_dct_pred[3];
  int PMV[2][2][2], motion_vertical_field_select[2][2];
  int dmvector[2];
  int stwtype, stwclass;
  int SNRMBA, SNRMBAinc;
  int ret;

  MBA = 0; /* macroblock address */
  MBAinc = 0;

  if((ret=start_of_slice(MBAmax, &MBA, &MBAinc, dc_dct_pred, PMV))!=1)
    return(ret);

  if (Two_Streams && enhan.scalable_mode==SC_SNR)
  {
    SNRMBA=0;
    SNRMBAinc=0;
  }

  Fault_Flag=0;

  for (;;)
  {

    /* this is how we properly exit out of picture */
    if (MBA>=MBAmax)
      return(-1); /* all macroblocks decoded */

#ifdef TRACE
    if (Trace_Flag)
      printf("frame %d, MB %d\n",framenum,MBA);
#endif /* TRACE */

#ifdef DISPLAY
    if (!progressive_frame && picture_structure==FRAME_PICTURE 
      && MBA==(MBAmax>>1) && framenum!=0 && Output_Type==T_X11 
       && !Display_Progressive_Flag)
    {
      Display_Second_Field();
    }
#endif

    ld = &base;

    if (MBAinc==0)
    {
      if (base.scalable_mode==SC_DP && base.priority_breakpoint==1)
          ld = &enhan;

      if (!Show_Bits(23) || Fault_Flag) /* next_start_code or fault */
      {
resync: /* if Fault_Flag: resynchronize to next next_start_code */
        Fault_Flag = 0;
        return(0);     /* trigger: go to next slice */
      }
      else /* neither next_start_code nor Fault_Flag */
      {
        if (base.scalable_mode==SC_DP && base.priority_breakpoint==1)
          ld = &enhan;

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

        if (Fault_Flag) goto resync;
      }
    }

    if (MBA>=MBAmax)
    {
      /* MBAinc points beyond picture dimensions */
      if (!Quiet_Flag)
        printf("Too many macroblocks in picture\n");
      return(-1);
    }

    if (MBAinc==1) /* not skipped */
    {
      ret = decode_macroblock(&macroblock_type, &stwtype, &stwclass,
              &motion_type, &dct_type, PMV, dc_dct_pred, 
              motion_vertical_field_select, dmvector);

      if(ret==-1)
        return(-1);
   
      if(ret==0)
        goto resync;

    }
    else /* MBAinc!=1: skipped macroblock */
    {      
      /* ISO/IEC 13818-2 section 7.6.6 */
      skipped_macroblock(dc_dct_pred, PMV, &motion_type, 
        motion_vertical_field_select, &stwtype, &macroblock_type);
    }

    /* SCALABILITY: SNR */
    /* ISO/IEC 13818-2 section 7.8 */
    /* NOTE: we currently ignore faults encountered in this routine */
    if (Two_Streams && enhan.scalable_mode==SC_SNR)
      Decode_SNR_Macroblock(&SNRMBA, &SNRMBAinc, MBA, MBAmax, &dct_type);

    /* ISO/IEC 13818-2 section 7.6 */
    motion_compensation(MBA, macroblock_type, motion_type, PMV, 
      motion_vertical_field_select, dmvector, stwtype, dct_type);


    /* advance to next macroblock */
    MBA++;
    MBAinc--;
 
    /* SCALABILITY: SNR */
    if (Two_Streams && enhan.scalable_mode==SC_SNR)
    {
      SNRMBA++;
      SNRMBAinc--;
    }

    if (MBA>=MBAmax)
      return(-1); /* all macroblocks decoded */
  }
}

 
/* ISO/IEC 13818-2 section 6.3.17.1: Macroblock modes */
static void macroblock_modes(pmacroblock_type,pstwtype,pstwclass,
  pmotion_type,pmotion_vector_count,pmv_format,pdmv,pmvscale,pdct_type)
  int *pmacroblock_type, *pstwtype, *pstwclass;
  int *pmotion_type, *pmotion_vector_count, *pmv_format, *pdmv, *pmvscale;
  int *pdct_type;
{
  int macroblock_type;
  int stwtype, stwcode, stwclass;
  int motion_type = 0;
  int motion_vector_count, mv_format, dmv, mvscale;
  int dct_type;
  static unsigned char stwc_table[3][4]
    = { {6,3,7,4}, {2,1,5,4}, {2,5,7,4} };
  static unsigned char stwclass_table[9]
    = {0, 1, 2, 1, 1, 2, 3, 3, 4};

  /* get macroblock_type */
  macroblock_type = Get_macroblock_type();

  if (Fault_Flag) return;

  /* get spatial_temporal_weight_code */
  if (macroblock_type & MB_WEIGHT)
  {
    if (spatial_temporal_weight_code_table_index==0)
      stwtype = 4;
    else
    {
      stwcode = Get_Bits(2);
#ifdef TRACE
      if (Trace_Flag)
      {
        printf("spatial_temporal_weight_code (");
        Print_Bits(stwcode,2,2);
        printf("): %d\n",stwcode);
      }
#endif /* TRACE */
      stwtype = stwc_table[spatial_temporal_weight_code_table_index-1][stwcode];
    }
  }
  else
    stwtype = (macroblock_type & MB_CLASS4) ? 8 : 0;

  /* SCALABILITY: derive spatial_temporal_weight_class (Table 7-18) */
  stwclass = stwclass_table[stwtype];

  /* get frame/field motion type */
  if (macroblock_type & (MACROBLOCK_MOTION_FORWARD|MACROBLOCK_MOTION_BACKWARD))
  {
    if (picture_structure==FRAME_PICTURE) /* frame_motion_type */
    {
      motion_type = frame_pred_frame_dct ? MC_FRAME : Get_Bits(2);
#ifdef TRACE
      if (!frame_pred_frame_dct && Trace_Flag)
      {
        printf("frame_motion_type (");
        Print_Bits(motion_type,2,2);
        printf("): %s\n",motion_type==MC_FIELD?"Field":
                         motion_type==MC_FRAME?"Frame":
                         motion_type==MC_DMV?"Dual_Prime":"Invalid");
      }
#endif /* TRACE */
    }
    else /* field_motion_type */
    {
      motion_type = Get_Bits(2);
#ifdef TRACE
      if (Trace_Flag)
      {
        printf("field_motion_type (");
        Print_Bits(motion_type,2,2);
        printf("): %s\n",motion_type==MC_FIELD?"Field":
                         motion_type==MC_16X8?"16x8 MC":
                         motion_type==MC_DMV?"Dual_Prime":"Invalid");
      }
#endif /* TRACE */
    }
  }
  else if ((macroblock_type & MACROBLOCK_INTRA) && concealment_motion_vectors)
  {
    /* concealment motion vectors */
    motion_type = (picture_structure==FRAME_PICTURE) ? MC_FRAME : MC_FIELD;
  }
#if 0
  else
  {
    printf("maroblock_modes(): unknown macroblock type\n");
    motion_type = -1;
  }
#endif

  /* derive motion_vector_count, mv_format and dmv, (table 6-17, 6-18) */
  if (picture_structure==FRAME_PICTURE)
  {
    motion_vector_count = (motion_type==MC_FIELD && stwclass<2) ? 2 : 1;
    mv_format = (motion_type==MC_FRAME) ? MV_FRAME : MV_FIELD;
  }
  else
  {
    motion_vector_count = (motion_type==MC_16X8) ? 2 : 1;
    mv_format = MV_FIELD;
  }

  dmv = (motion_type==MC_DMV); /* dual prime */

  /* field mv predictions in frame pictures have to be scaled
   * ISO/IEC 13818-2 section 7.6.3.1 Decoding the motion vectors
   * IMPLEMENTATION: mvscale is derived for later use in motion_vectors()
   * it displaces the stage:
   *
   *    if((mv_format=="field")&&(t==1)&&(picture_structure=="Frame picture"))
   *      prediction = PMV[r][s][t] DIV 2;
   */

  mvscale = ((mv_format==MV_FIELD) && (picture_structure==FRAME_PICTURE));

  /* get dct_type (frame DCT / field DCT) */
  dct_type = (picture_structure==FRAME_PICTURE)
             && (!frame_pred_frame_dct)
             && (macroblock_type & (MACROBLOCK_PATTERN|MACROBLOCK_INTRA))
             ? Get_Bits(1)
             : 0;

#ifdef TRACE
  if (Trace_Flag  && (picture_structure==FRAME_PICTURE)
             && (!frame_pred_frame_dct)
             && (macroblock_type & (MACROBLOCK_PATTERN|MACROBLOCK_INTRA)))
    printf("dct_type (%d): %s\n",dct_type,dct_type?"Field":"Frame");
#endif /* TRACE */

  /* return values */
  *pmacroblock_type = macroblock_type;
  *pstwtype = stwtype;
  *pstwclass = stwclass;
  *pmotion_type = motion_type;
  *pmotion_vector_count = motion_vector_count;
  *pmv_format = mv_format;
  *pdmv = dmv;
  *pmvscale = mvscale;