/* systems.c, 系統參數設置程序*/#include <stdio.h>#include <stdlib.h>#include "config.h"#include "global.h"/* initialize buffer, call once before first getbits or showbits *//* parse system layer, ignore everything we don't need */void Next_Packet(){  unsigned int code;  int l;  for(;;)  {    code = Get_Long();    /* remove system layer byte stuffing */    while ((code & 0xffffff00) != 0x100)      code = (code<<8) | Get_Byte();    switch(code)    {    case PACK_START_CODE: /* pack header */      /* skip pack header (system_clock_reference and mux_rate) */      ld->Rdptr += 8;      break;    case VIDEO_ELEMENTARY_STREAM:         code = Get_Word();             /* packet_length */      ld->Rdmax = ld->Rdptr + code;      code = Get_Byte();      if((code>>6)==0x02)      {        ld->Rdptr++;        code=Get_Byte();  /* parse PES_header_data_length */        ld->Rdptr+=code;    /* advance pointer by PES_header_data_length */        printf("MPEG-2 PES packet\n");        return;      }      else if(code==0xff)      {        /* parse MPEG-1 packet header */        while((code=Get_Byte())== 0xFF);      }             /* stuffing bytes */      if(code>=0x40)      {        if(code>=0x80)        {          fprintf(stderr,"Error in packet header\n");          exit(1);        }        /* skip STD_buffer_scale */        ld->Rdptr++;        code = Get_Byte();      }      if(code>=0x30)      {        if(code>=0x40)        {          fprintf(stderr,"Error in packet header\n");          exit(1);        }        /* skip presentation and decoding time stamps */        ld->Rdptr += 9;      }      else if(code>=0x20)      {        /* skip presentation time stamps */        ld->Rdptr += 4;      }      else if(code!=0x0f)      {        fprintf(stderr,"Error in packet header\n");        exit(1);      }      return;    case ISO_END_CODE: /* end */      /* simulate a buffer full of sequence end codes */      l = 0;      while (l<2048)      {        ld->Rdbfr[l++] = SEQUENCE_END_CODE>>24;        ld->Rdbfr[l++] = SEQUENCE_END_CODE>>16;        ld->Rdbfr[l++] = SEQUENCE_END_CODE>>8;        ld->Rdbfr[l++] = SEQUENCE_END_CODE&0xff;      }      ld->Rdptr = ld->Rdbfr;      ld->Rdmax = ld->Rdbfr + 2048;      return;    default:      if(code>=SYSTEM_START_CODE)      {        /* skip system headers and non-video packets*/        code = Get_Word();        ld->Rdptr += code;      }      else      {        fprintf(stderr,"Unexpected startcode %08x in system layer\n",code);        exit(1);      }      break;    }  }}void Flush_Buffer32(){  int Incnt;  ld->Bfr = 0;  Incnt = ld->Incnt;  Incnt -= 32;  if (System_Stream_Flag && (ld->Rdptr >= ld->Rdmax-4))  {    while (Incnt <= 24)    {      if (ld->Rdptr >= ld->Rdmax)        Next_Packet();      ld->Bfr |= Get_Byte() << (24 - Incnt);      Incnt += 8;    }  }  else  {    while (Incnt <= 24)    {      if (ld->Rdptr >= ld->Rdbfr+2048)        Fill_Buffer();      ld->Bfr |= *ld->Rdptr++ << (24 - Incnt);      Incnt += 8;    }  }  ld->Incnt = Incnt;#ifdef VERIFY   ld->Bitcnt += 32;#endif /* VERIFY */}unsigned int Get_Bits32(){  unsigned int l;  l = Show_Bits(32);  Flush_Buffer32();  return l;}int Get_Long(){  int i;  i = Get_Word();  return (i<<16) | Get_Word();}