gethdr.c

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

/* gethdr.c, header decoding                                                */

/* Copyright (C) 1994, 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 int gethdr _ANSI_ARGS_((void));
static void getseqhdr _ANSI_ARGS_((void));
static void getgophdr _ANSI_ARGS_((void));
static void getpicturehdr _ANSI_ARGS_((void));
static void ext_user_data _ANSI_ARGS_((void));
static void sequence_extension _ANSI_ARGS_((void));
static void sequence_display_extension _ANSI_ARGS_((void));
static void quant_matrix_extension _ANSI_ARGS_((void));
static void sequence_scalable_extension _ANSI_ARGS_((void));
static void picture_display_extension _ANSI_ARGS_((void));
static void picture_coding_extension _ANSI_ARGS_((void));
static void picture_spatial_scalable_extension _ANSI_ARGS_((void));
static void picture_temporal_scalable_extension _ANSI_ARGS_((void));
static void ext_bit_info _ANSI_ARGS_((void));


/* decode headers from all input streams */

int getheader()
{
  int ret;

  ld = &base;
  ret = gethdr();
  if (twostreams)
  {
    ld = &enhan;
    if (gethdr()!=ret && !quiet)
      fprintf(stderr,"streams out of sync\n");
    ld = &base;
  }

  return ret;
}


/*
 * decode headers from one input stream
 * until an End of Sequence or picture start code
 * is found
 */

static int gethdr()
{
  unsigned int code;

  for (;;)
  {
    /* look for startcode */
    startcode();
    code = getbits(32);
    switch (code)
    {
    case SEQ_START_CODE:
      getseqhdr();
      break;
    case GOP_START_CODE:
      getgophdr();
      break;
    case PICTURE_START_CODE:
      getpicturehdr();
      return 1;
      break;
    case SEQ_END_CODE:
      return 0;
      break;
    default:
      if (!quiet)
        fprintf(stderr,"Unexpected startcode %08x (ignored)\n",code);
      break;
    }
  }
}


/* align to start of next startcode */

void startcode()
{
  /* byte align */
  flushbits(ld->incnt&7);
  while (showbits(24)!=1l)
    flushbits(8);
}


/* decode sequence header */

static void getseqhdr()
{
  int i;
  int constrained_parameters_flag;
  int load_intra_quantizer_matrix, load_non_intra_quantizer_matrix;
  int pos;

  pos = ld->bitcnt;
  horizontal_size = getbits(12);
  vertical_size = getbits(12);
  aspect_ratio = getbits(4);
  picture_rate = getbits(4);
  bit_rate_value = getbits(18);
  flushbits(1); /* marker bit (=1) */
  vbv_buffer_size = getbits(10);
  constrained_parameters_flag = getbits(1);

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

  if (load_non_intra_quantizer_matrix = getbits(1))
  {
    for (i=0; i<64; i++)
      ld->non_intra_quantizer_matrix[zig_zag_scan[i]] = getbits(8);
  }
  else
  {
    for (i=0; i<64; i++)
      ld->non_intra_quantizer_matrix[i] = 16;
  }

  /* copy luminance to chrominance matrices */
  for (i=0; i<64; i++)
  {
    ld->chroma_intra_quantizer_matrix[i] =
      ld->intra_quantizer_matrix[i];

    ld->chroma_non_intra_quantizer_matrix[i] =
      ld->non_intra_quantizer_matrix[i];
  }

  if (verbose>0)
  {
    printf("sequence header (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      printf("  horizontal_size=%d\n",horizontal_size);
      printf("  vertical_size=%d\n",vertical_size);
      printf("  aspect_ratio=%d\n",aspect_ratio);
      printf("  picture_rate=%d\n",picture_rate);
      printf("  bit_rate_value=%d\n",bit_rate_value);
      printf("  vbv_buffer_size=%d\n",vbv_buffer_size);
      printf("  constrained_parameters_flag=%d\n",constrained_parameters_flag);
      printf("  load_intra_quantizer_matrix=%d\n",load_intra_quantizer_matrix);
      printf("  load_non_intra_quantizer_matrix=%d\n",load_non_intra_quantizer_matrix);
    }
  }

  ext_user_data();
}


/* decode group of pictures header */

static void getgophdr()
{
  int drop_flag, hour, minute, sec, frame, closed_gop, broken_link;
  int pos;

  pos = ld->bitcnt;
  drop_flag = getbits(1);
  hour = getbits(5);
  minute = getbits(6);
  flushbits(1);
  sec = getbits(6);
  frame = getbits(6);
  closed_gop = getbits(1);
  broken_link = getbits(1);

  if (verbose>0)
  {
    printf("group of pictures (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      printf("  drop_flag=%d\n",drop_flag);
      printf("  timecode %d:%02d:%02d:%02d\n",hour,minute,sec,frame);
      printf("  closed_gop=%d\n",closed_gop);
      printf("  broken_link=%d\n",broken_link);
    }
  }

  ext_user_data();
}


/* decode picture header */

static void getpicturehdr()
{
  int pos;

  ld->pict_scal = 0; /* unless overwritten by pict. spat. scal. ext. */

  pos = ld->bitcnt;
  temp_ref = getbits(10);
  pict_type = getbits(3);
  vbv_delay = getbits(16);
  if (pict_type==P_TYPE || pict_type==B_TYPE)
  {
    full_forw = getbits(1);
    forw_r_size = getbits(3) - 1;
  }
  if (pict_type==B_TYPE)
  {
    full_back = getbits(1);
    back_r_size = getbits(3) - 1;
  }

  if (verbose>0)
  {
    printf("picture header (byte %d)\n",(pos>>3)-4);
    if (verbose>1)
    {
      printf("  temp_ref=%d\n",temp_ref);
      printf("  pict_type=%d\n",pict_type);
      printf("  vbv_delay=%d\n",vbv_delay);
      if (pict_type==P_TYPE || pict_type==B_TYPE)
      {
        printf("  full_forw=%d\n",full_forw);
        printf("  forw_r_size=%d\n",forw_r_size);
      }
      if (pict_type==B_TYPE)
      {
        printf("  full_back=%d\n",full_back);
        printf("  back_r_size=%d\n",back_r_size);
      }
    }
  }

  ext_bit_info();
  ext_user_data();
}

/* decode slice header */

int getslicehdr()
{
  int slice_vertical_position_extension;
  int qs;
  int pos;

  pos = ld->bitcnt;
  slice_vertical_position_extension =
    (ld->mpeg2 && vertical_size>2800) ? getbits(3) : 0;

  if (ld->scalable_mode==SC_DP)
    ld->pri_brk = getbits(7);

  qs = getbits(5);
  ld->quant_scale =
    ld->mpeg2 ? (ld->qscale_type ? non_linear_mquant_table[qs] : qs<<1) : qs;

  if (getbits(1))
  {
    ld->intra_slice = getbits(1);
    flushbits(7);
    ext_bit_info();
  }
  else
    ld->intra_slice = 0;

  if (verbose>2)
  {
    printf("slice header (byte %d)\n",(pos>>3)-4);
    if (verbose>3)
    {
      if (ld->mpeg2 && vertical_size>2800)
        printf("  slice_vertical_position_extension=%d\n",slice_vertical_position_extension);
      if (ld->scalable_mode==SC_DP)
        printf("  priority_breakpoint=%d\n",ld->pri_brk);
      printf("  quantizer_scale_code=%d\n",qs);
    }
  }
  return slice_vertical_position_extension;
}


/* decode extension and user data */

static void ext_user_data()
{
  int code,ext_ID;

  startcode();

  while ((code = showbits(32))==EXT_START_CODE || code==USER_START_CODE)
  {
    if (code==EXT_START_CODE)
    {
      flushbits(32);
      ext_ID = getbits(4);
      switch (ext_ID)
      {
      case SEQ_ID:
        sequence_extension();
        break;
      case DISP_ID:
        sequence_display_extension();
        break;
      case QUANT_ID:
        quant_matrix_extension();
        break;
      case SEQSCAL_ID:
        sequence_scalable_extension();
        break;
      case PANSCAN_ID:
        picture_display_extension();
        break;
      case CODING_ID:
        picture_coding_extension();
        break;
      case SPATSCAL_ID:
        picture_spatial_scalable_extension();
        break;
      case TEMPSCAL_ID:
        picture_temporal_scalable_extension();
        break;
      default:
        fprintf(stderr,"reserved extension start code ID %d\n",ext_ID);
        break;
      }
      startcode();
    }
    else
    {
      if (verbose)
        printf("user data\n");
      flushbits(32);
      startcode();
    }
  }
}