decoder.c

MPEG-4编解码的实现(包括MPEG4视音频编解码)

      if (dx == 1) {
        result = (result + imY[pres_y][max(0,min(maxold_x,x_pos))])/2;
      }
      else if (dx == 3) {
        result = (result + imY[pres_y][max(0,min(maxold_x,x_pos+1))])/2;
      }
    }
    else if (dx == 0) {

      pres_x = max(0,min(maxold_x,x_pos));
      for(y=-2;y<4;y++) {
        pres_y = max(0,min(maxold_y,y_pos+y));
        result += imY[pres_y][pres_x]*COEF[y+2];
      }

      result = max(0, min(255, (result+16)/32));

      if (dy == 1) {
        result = (result + imY[max(0,min(maxold_y,y_pos))][pres_x])/2;
      }
      else if (dy == 3) {
        result = (result + imY[max(0,min(maxold_y,y_pos+1))][pres_x])/2;
      }
    }
    else if (dx == 2) {

      for(y=-2;y<4;y++) {
        result = 0;
        pres_y = max(0,min(maxold_y,y_pos+y));
        for(x=-2;x<4;x++) {
          pres_x = max(0,min(maxold_x,x_pos+x));
          result += imY[pres_y][pres_x]*COEF[x+2];
        }
        tmp_res[y+2] = result;
      }

      result = 0;
      for(y=-2;y<4;y++) {
        result += tmp_res[y+2]*COEF[y+2];
      }

      result = max(0, min(255, (result+512)/1024));

      if (dy == 1) {
        result = (result + max(0, min(255, (tmp_res[2]+16)/32)))/2;
      }
      else if (dy == 3) {
        result = (result + max(0, min(255, (tmp_res[3]+16)/32)))/2;
      }
    }
    else if (dy == 2) {

      for(x=-2;x<4;x++) {
        result = 0;
        pres_x = max(0,min(maxold_x,x_pos+x));
        for(y=-2;y<4;y++) {
          pres_y = max(0,min(maxold_y,y_pos+y));
          result += imY[pres_y][pres_x]*COEF[y+2];
        }
        tmp_res[x+2] = result;
      }

      result = 0;
      for(x=-2;x<4;x++) {
        result += tmp_res[x+2]*COEF[x+2];
      }

      result = max(0, min(255, (result+512)/1024));

      if (dx == 1) {
        result = (result + max(0, min(255, (tmp_res[2]+16)/32)))/2;
      }
      else {
        result = (result + max(0, min(255, (tmp_res[3]+16)/32)))/2;
      }
    }
    else {

      result = 0;
      pres_y = dy == 1 ? y_pos : y_pos+1;
      pres_y = max(0,min(maxold_y,pres_y));

      for(x=-2;x<4;x++) {
        pres_x = max(0,min(maxold_x,x_pos+x));
        result += imY[pres_y][pres_x]*COEF[x+2];
      }

      result1 = max(0, min(255, (result+16)/32));

      result = 0;
      pres_x = dx == 1 ? x_pos : x_pos+1;
      pres_x = max(0,min(maxold_x,pres_x));

      for(y=-2;y<4;y++) {
        pres_y = max(0,min(maxold_y,y_pos+y));
        result += imY[pres_y][pres_x]*COEF[y+2];
      }

      result2 = max(0, min(255, (result+16)/32));
      result = (result1+result2)/2;
    }
  }

  return result;
}
  
/*! 
 *************************************************************************************
 * \brief
 *    Performs the simulation of the packet losses, calls the error concealment funcs
 *    and copies the decoded images to the reference frame buffers of the decoders 
 *
 *************************************************************************************
 */
void UpdateDecoders()
{
  int k;
  for (k=0; k<input->NoOfDecoders; k++)
  {
    Build_Status_Map(status_map); // simulates the packet losses
    Error_Concealment(decY_best[k], status_map, decref[k]); // for the moment error concealment is just a "copy"
    // Move decoded frames to reference buffers: (at the decoders this is done 
    // without interpolation (upsampling) - upsampling is done while decoding
    DecOneForthPix(decY_best[k], decref[k]); 
  }
}
/*! 
 *************************************************************************************
 * \brief
 *    Copies one (reconstructed) image to the respective reference frame buffer
 *
 * \note
 *    This is used at the "many decoders in the encoder"
 * \param dY
 *    The reconstructed image
 * \param dref
 *    The reference buffer
 *************************************************************************************
 */
void DecOneForthPix(byte **dY, byte ***dref)
{
  int j, ref=img->number%img->buf_cycle;

  for (j=0; j<img->height; j++)
    memcpy(dref[ref][j], dY[j], img->width);
}

/*! 
 *************************************************************************************
 * \brief
 *    Gives the prediction residue for this MB.
 *
 * \param mode
 *    The encoding mode of this MB.
 *************************************************************************************
 */
void compute_residue(int mode)
{
  int i,j;
  if (mode == MBMODE_INTRA16x16)  /* Intra 16 MB*/
    for (i=0; i<MB_BLOCK_SIZE; i++)
      for (j=0; j<MB_BLOCK_SIZE; j++)
        resY[j][i] = imgY[img->pix_y+j][img->pix_x+i]-img->mprr_2[mode][j][i]; /* SOS: Is this correct? or maybe mprr_2[][i][j] ??*/
  else
    for (i=0; i<MB_BLOCK_SIZE; i++)  /* Inter MB */
      for (j=0; j<MB_BLOCK_SIZE; j++)
        resY[j][i] = imgY[img->pix_y+j][img->pix_x+i]-img->mpr[i][j];
}

/*! 
 *************************************************************************************
 * \brief
 *    Builds a random status map showing whether each MB is received or lost, based
 *    on the packet loss rate and the slice structure.
 *
 * \param s_map
 *    The status map to be filled
 *************************************************************************************
 */
void Build_Status_Map(byte **s_map)
{
  int i,j,slice=-1,mb=0,jj,ii,packet_lost;

  jj = img->height/MB_BLOCK_SIZE;
  ii = img->width/MB_BLOCK_SIZE;

  for (j=0 ; j<jj; j++)
    for (i=0 ; i<ii; i++)
    {
      if (!input->slice_mode || img->mb_data[mb].slice_nr != slice) /* new slice */
      {
        if ((double)rand()/(double)RAND_MAX*100 < input->LossRate)
          packet_lost=1;
        else
          packet_lost=0;
        
        slice++;
      }
      if (packet_lost)
        s_map[j][i]=0;
      else
        s_map[j][i]=1;
      mb++;
    }
}

/*! 
 *************************************************************************************
 * \brief
 *    Performs some sort of error concealment for the areas that are lost according
 *    to the status_map
 *    
 * \param inY
 *    Error concealment is performed on this frame imY[][]
 * \param s_map
 *    The status map shows which areas are lost.
 * \param refY
 *    The set of reference frames - may be used for the error concealment.
 *************************************************************************************
 */
void Error_Concealment(byte **inY, byte **s_map, byte ***refY)
{
  int mb_y, mb_x, mb_h, mb_w;
  mb_h = img->height/MB_BLOCK_SIZE;
  mb_w = img->width/MB_BLOCK_SIZE;
  
  for (mb_y=0; mb_y < mb_h; mb_y++)
    for (mb_x=0; mb_x < mb_w; mb_x++)
      if (!s_map[mb_y][mb_x])
        Conceal_Error(inY, mb_y, mb_x, refY);
}

/*! 
 *************************************************************************************
 * \brief
 *    Copies a certain MB (mb_y,mb_x) of the frame inY[][] from the previous frame.
 *    For the time there is no better EC...
 *************************************************************************************
 */
void Conceal_Error(byte **inY, int mb_y, int mb_x, byte ***refY)
{
  int i,j;
  int ref_inx = (img->number-1)%img->no_multpred;
  int pos_y = mb_y*MB_BLOCK_SIZE, pos_x = mb_x*MB_BLOCK_SIZE;
  if (img->number)
  {
    for (j=0;j<MB_BLOCK_SIZE;j++)
      for (i=0;i<MB_BLOCK_SIZE;i++)
        inY[pos_y+j][pos_x+i] = refY[ref_inx][pos_y+j][pos_x+i];
  }
  else
  {
    for (j=0;j<MB_BLOCK_SIZE;j++)
      for (i=0;i<MB_BLOCK_SIZE;i++)
        inY[pos_y+j][pos_x+i] = 127;
  }
}