gethdr.c

MPEG-2 has 7 distinct parts as well. The first part is the Systems section which defines the contain

/* decode sequence extension */

static void sequence_extension()
{
  int prof_lev;
  int horizontal_size_extension, vertical_size_extension;
  int bit_rate_extension, vbv_buffer_size_extension;
  int frame_rate_extension_n, frame_rate_extension_d;
  int pos;

  pos = ld->bitcnt;
  ld->mpeg2 = 1;
  ld->scalable_mode = SC_NONE; /* unless overwritten by seq. scal. ext. */
  prof_lev = getbits(8);
  prog_seq = getbits(1);
  chroma_format = getbits(2);
  horizontal_size_extension = getbits(2);
  vertical_size_extension = getbits(2);
  bit_rate_extension = getbits(12);
  flushbits(1);
  vbv_buffer_size_extension = getbits(8);
  low_delay = getbits(1);
  frame_rate_extension_n = getbits(2);
  frame_rate_extension_d = getbits(5);

  profile = prof_lev >> 4;  /* Profile is upper nibble */
  level = prof_lev & 15;    /* Level is lower nibble */
  horizontal_size = (horizontal_size_extension<<12) | (horizontal_size&0x0fff);
  vertical_size = (vertical_size_extension<<12) | (vertical_size&0x0fff);
  bit_rate = (float) ((bit_rate_extension << 18) + bit_rate_value) * 400.0;

  if (verbose>0)
  {
    printf("sequence extension (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      printf("  profile_and_level_indication=%d\n",prof_lev);
      if (prof_lev<128)
      {
        printf("    profile=%d, level=%d\n",profile,level);
      }
      printf("  progressive_sequence=%d\n",prog_seq);
      printf("  chroma_format=%d\n",chroma_format);
      printf("  horizontal_size_extension=%d\n",horizontal_size_extension);
      printf("  vertical_size_extension=%d\n",vertical_size_extension);
      printf("  bit_rate_extension=%d\n",bit_rate_extension);
      printf("  vbv_buffer_size_extension=%d\n",vbv_buffer_size_extension);
      printf("  low_delay=%d\n",low_delay);
      printf("  frame_rate_extension_n=%d\n",frame_rate_extension_n);
      printf("  frame_rate_extension_d=%d\n",frame_rate_extension_d);
    }
  }
}


/* decode sequence display extension */

static void sequence_display_extension()
{
  int colour_description;
  int pos;

  pos = ld->bitcnt;
  video_format = getbits(3);
  colour_description = getbits(1);

  if (colour_description)
  {
    colour_primaries = getbits(8);
    transfer_characteristics = getbits(8);
    matrix_coefficients = getbits(8);
  }

  display_horizontal_size = getbits(14);
  flushbits(1);
  display_vertical_size = getbits(14);

  if (verbose>0)
  {
    printf("sequence display extension (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      printf("  video_format=%d\n",video_format);
      printf("  colour_description=%d\n",colour_description);
      if (colour_description)
      {
        printf("    colour_primaries=%d\n",colour_primaries);
        printf("    transfer_characteristics=%d\n",transfer_characteristics);
        printf("    matrix_coefficients=%d\n",matrix_coefficients);
      }
      printf("  display_horizontal_size=%d\n",display_horizontal_size);
      printf("  display_vertical_size=%d\n",display_vertical_size);
    }
  }
}


/* decode quant matrix entension */

static void quant_matrix_extension()
{
  int i;
  int load_intra_quantiser_matrix, load_non_intra_quantiser_matrix;
  int load_chroma_intra_quantiser_matrix;
  int load_chroma_non_intra_quantiser_matrix;
  int pos;

  pos = ld->bitcnt;

  if (load_intra_quantiser_matrix = getbits(1))
  {
    for (i=0; i<64; i++)
    {
      ld->chroma_intra_quantizer_matrix[zig_zag_scan[i]]
      = ld->intra_quantizer_matrix[zig_zag_scan[i]]
      = getbits(8);
    }
  }

  if (load_non_intra_quantiser_matrix = getbits(1))
  {
    for (i=0; i<64; i++)
    {
      ld->chroma_non_intra_quantizer_matrix[zig_zag_scan[i]]
      = ld->non_intra_quantizer_matrix[zig_zag_scan[i]]
      = getbits(8);
    }
  }

  if (load_chroma_intra_quantiser_matrix = getbits(1))
  {
    for (i=0; i<64; i++)
      ld->chroma_intra_quantizer_matrix[zig_zag_scan[i]] = getbits(8);
  }

  if (load_chroma_non_intra_quantiser_matrix = getbits(1))
  {
    for (i=0; i<64; i++)
      ld->chroma_non_intra_quantizer_matrix[zig_zag_scan[i]] = getbits(8);
  }

  if (verbose>0)
  {
    printf("quant matrix extension (byte %d)\n",(pos>>3)-4);
    printf("  load_intra_quantiser_matrix=%d\n",
      load_intra_quantiser_matrix);
    printf("  load_non_intra_quantiser_matrix=%d\n",
      load_non_intra_quantiser_matrix);
    printf("  load_chroma_intra_quantiser_matrix=%d\n",
      load_chroma_intra_quantiser_matrix);
    printf("  load_chroma_non_intra_quantiser_matrix=%d\n",
      load_chroma_non_intra_quantiser_matrix);
  }
}


/* decode sequence scalable extension */

static void sequence_scalable_extension()
{
  int layer_id;
  int pos;

  pos = ld->bitcnt;
  ld->scalable_mode = getbits(2) + 1; /* add 1 to make SC_DP != SC_NONE */
  layer_id = getbits(4);

  if (ld->scalable_mode==SC_SPAT)
  {
    llw = getbits(14); /* lower_layer_prediction_horizontal_size */
    flushbits(1);
    llh = getbits(14); /* lower_layer_prediction_vertical_size */
    hm = getbits(5);
    hn = getbits(5);
    vm = getbits(5);
    vn = getbits(5);
  }

  if (ld->scalable_mode==SC_TEMP)
    error("temporal scalability not implemented\n");

  if (verbose>0)
  {
    printf("sequence scalable extension (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      printf("  scalable_mode=%d\n",ld->scalable_mode-1);
      printf("  layer_id=%d\n",layer_id);
      if (ld->scalable_mode==SC_SPAT)
      {
        printf("    lower_layer_prediction_horiontal_size=%d\n",llw);
        printf("    lower_layer_prediction_vertical_size=%d\n",llh);
        printf("    horizontal_subsampling_factor_m=%d\n",hm);
        printf("    horizontal_subsampling_factor_n=%d\n",hn);
        printf("    vertical_subsampling_factor_m=%d\n",vm);
        printf("    vertical_subsampling_factor_n=%d\n",vn);
      }
    }
  }
}


/* decode picture display extension */

static void picture_display_extension()
{
  int i,n;
  short frame_centre_horizontal_offset[3];
  short frame_centre_vertical_offset[3];
  int pos;

  pos = ld->bitcnt;

  if (prog_seq || pict_struct!=FRAME_PICTURE)
    n = 1;
  else
    n = repeatfirst ? 3 : 2;

  for (i=0; i<n; i++)
  {
    frame_centre_horizontal_offset[i] = (short)getbits(16);
    flushbits(1);
    frame_centre_vertical_offset[i] = (short)getbits(16);
    flushbits(1);
  }

  if (verbose>0)
  {
    printf("picture display extension (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      for (i=0; i<n; i++)
      {
        printf("  frame_centre_horizontal_offset[%d]=%d\n",i,
          frame_centre_horizontal_offset[i]);
        printf("  frame_centre_vertical_offset[%d]=%d\n",i,
          frame_centre_vertical_offset[i]);
      }
    }
  }
}


/* decode picture coding extension */

static void picture_coding_extension()
{
  int chroma_420_type, composite_display_flag;
  int v_axis, field_sequence, sub_carrier, burst_amplitude, sub_carrier_phase;
  int pos;

  pos = ld->bitcnt;

  h_forw_r_size = getbits(4) - 1;
  v_forw_r_size = getbits(4) - 1;
  h_back_r_size = getbits(4) - 1;
  v_back_r_size = getbits(4) - 1;
  dc_prec = getbits(2);
  pict_struct = getbits(2);
  topfirst = getbits(1);
  frame_pred_dct = getbits(1);
  conceal_mv = getbits(1);
  ld->qscale_type = getbits(1);
  intravlc = getbits(1);
  ld->altscan = getbits(1);
  repeatfirst = getbits(1);
  chroma_420_type = getbits(1);
  prog_frame = getbits(1);
  composite_display_flag = getbits(1);
  if (composite_display_flag)
  {
    v_axis = getbits(1);
    field_sequence = getbits(3);
    sub_carrier = getbits(1);
    burst_amplitude = getbits(7);
    sub_carrier_phase = getbits(8);
  }

  if (verbose>0)
  {
    printf("picture coding extension (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      printf("  forward_horizontal_f_code=%d\n",h_forw_r_size+1);
      printf("  forward_vertical_f_code=%d\n",v_forw_r_size+1);
      printf("  backward_horizontal_f_code=%d\n",h_back_r_size+1);
      printf("  backward_vertical_f_code=%d\n",v_back_r_size+1);
      printf("  intra_dc_precision=%d\n",dc_prec);
      printf("  picture_structure=%d\n",pict_struct);
      printf("  top_field_first=%d\n",topfirst);
      printf("  frame_pred_frame_dct=%d\n",frame_pred_dct);
      printf("  concealment_motion_vectors=%d\n",conceal_mv);
      printf("  q_scale_type=%d\n",ld->qscale_type);
      printf("  intra_vlc_format=%d\n",intravlc);
      printf("  alternate_scan=%d\n",ld->altscan);
      printf("  repeat_first_field=%d\n",repeatfirst);
      printf("  chroma_420_type=%d\n",chroma_420_type);
      printf("  progressive_frame=%d\n",prog_frame);
      printf("  composite_display_flag=%d\n",composite_display_flag);
      if (composite_display_flag)
      {
        printf("    v_axis=%d\n",v_axis);
        printf("    field_sequence=%d\n",field_sequence);
        printf("    sub_carrier=%d\n",sub_carrier);
        printf("    burst_amplitude=%d\n",burst_amplitude);
        printf("    sub_carrier_phase=%d\n",sub_carrier_phase);
      }
    }
  }
}


/* decode picture spatial scalable extension */

static void picture_spatial_scalable_extension()
{
  int pos;

  pos = ld->bitcnt;

  ld->pict_scal = 1; /* use spatial scalability in this picture */

  lltempref = getbits(10);
  flushbits(1);
  llx0 = getbits(15);
  if (llx0>=16384)
    llx0-= 32768;
  flushbits(1);
  lly0 = getbits(15);
  if (lly0>=16384)
    lly0-= 32768;
  stwc_table_index = getbits(2);
  llprog_frame = getbits(1);
  llfieldsel = getbits(1);
  if (verbose>0)
  {
    printf("picture spatial scalable extension (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      printf("  lower_layer_temporal_reference=%d\n",lltempref);
      printf("  lower_layer_horizontal_offset=%d\n",llx0);
      printf("  lower_layer_vertical_offset=%d\n",lly0);
      printf("  spatial_temporal_weight_code_table_index=%d\n",
        stwc_table_index);
      printf("  lower_layer_progressive_frame=%d\n",llprog_frame);
      printf("  lower_layer_deinterlaced_field_select=%d\n",llfieldsel);
    }
  }
}


/* decode picture temporal scalable extension
 *
 * not implemented
 */

static void picture_temporal_scalable_extension()
{
  error("temporal scalability not supported\n");
}


/* decode extra bit information */

static void ext_bit_info()
{
  while (getbits1())
    flushbits(8);
}