/* gethdr.c, header decoding                                                */

/*
 * tmndecode 
 * Copyright (C) 1995 Telenor R&D
 *                    Karl Olav Lillevold <kol@nta.no>                    
 *
 * based on mpeg2decode, (C) 1994, MPEG Software Simulation Group
 * and mpeg2play, (C) 1994 Stefan Eckart
 *                         <stefan@lis.e-technik.tu-muenchen.de>
 */


#include <stdio.h>

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

/* private prototypes */
static void getpicturehdr _ANSI_ARGS_((void));

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

int getheader()
{
  unsigned int code, gob;

  for (;;) {
    /* look for startcode */
    startcode();
    code = getbits(PSC_LENGTH);
    gob = getbits(5);
    if (gob == SEC) 
      return 0;
    if (gob == 0) {
      getpicturehdr();
      if (syntax_arith_coding)		/* reset decoder after receiving */
	decoder_reset();	        /* fixed length PSC string */
    }
    return gob + 1;
  }
}


/* align to start of next startcode */

void startcode()
{
  /* search for new picture start code */
  while (showbits(PSC_LENGTH)!=1l) 
  	 flushbits(1);
}

/* decode picture header */

static void getpicturehdr()
{
  int pos, pei, tmp;
  static int prev_temp_ref;

  pos = ld->bitcnt;
  prev_temp_ref = temp_ref;
  temp_ref = getbits(8);
  trd = temp_ref - prev_temp_ref;
  if (trd <= 0)
    trd += 256;
  tmp = getbits(1); /* always "1" */
  if (!tmp)
    if (!quiet)
      printf("warning: spare in picture header should be \"1\"\n");
  tmp = getbits(1); /* always "0" */
  if (tmp)
    if (!quiet)
      printf("warning: H.261 distinction bit should be \"0\"\n");
  tmp = getbits(1); /* split_screen_indicator */
  if (tmp) {
    if (!quiet)
      printf("warning: split-screen not supported in this version\n");
/*    exit (-1);   */
  }
  tmp = getbits(1); /* document_camera_indicator */
  if (tmp)
    if (!quiet)
      printf("warning: document camera indicator not supported in this version\n");

  tmp = getbits(1); /* freeze_picture_release */
  if (tmp)
    if (!quiet)
      printf("warning: frozen picture not supported in this version\n");

  source_format = getbits(3);
  source_format = 2;
  pict_type = getbits(1);
  mv_outside_frame = getbits(1);
  mv_outside_frame = 1;
  syntax_arith_coding = getbits(1);
  syntax_arith_coding = 0;
  adv_pred_mode = getbits(1);
  adv_pred_mode = 1;
  pb_frame = getbits(1);
  quant = getbits(5);
  tmp = getbits(1);
  if (tmp) {
    if (!quiet)
      printf("warning: CPM not supported in this version\n");
/*    exit(-1);   */
  }
  if (pb_frame) {
    trb = getbits(3);
    bquant = getbits(2);
    if(trb >= trd)
      trb = 1;
  }
  pei = getbits(1);
  if (pei)
    getbits(8);  /* extra info. (not used) */

  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("  source_format=%d\n", source_format);
      printf("  quant=%d\n",quant);
      if (syntax_arith_coding) 
    	printf("  SAC coding mode used \n");
      if (mv_outside_frame)
	printf("  unrestricted motion vector mode used\n");
      if (adv_pred_mode)
	printf("  advanced prediction mode used\n");
      if (pb_frame) {
	printf("  pb-frames mode used\n");
	printf("  trb=%d\n",trb);
	printf("  bquant=%d\n", bquant);
      }
    }
  }
}