H264码流中 分离和解析 nal

H.264码流解析的步骤就是首先从码流中搜索0x000001和0x00000001，

然后再分离出NALU；分析NALU的各个字段。

找到00 00 01 或 00 00 00 01

 if (3 != fread (Buf, 1, 3, h264bitstream)){          free(Buf);          return 0;      }      info2 = FindStartCode2 (Buf);      if(info2 != 1) {          if(1 != fread(Buf+3, 1, 1, h264bitstream)){              free(Buf);              return 0;          }          info3 = FindStartCode3 (Buf);          if (info3 != 1){               free(Buf);              return -1;          }          else {              pos = 4;              nalu->startcodeprefix_len = 4;          }      }      else{          nalu->startcodeprefix_len = 3;          pos = 3;      }      StartCodeFound = 0;      info2 = 0;      info3 = 0;  

分离NALU程序：

 static int FindStartCode2 (unsigned char *Buf){      if(Buf[0]!=0 || Buf[1]!=0 || Buf[2] !=1) return 0; //0x000001?      else return 1;  }    static int FindStartCode3 (unsigned char *Buf){      if(Buf[0]!=0 || Buf[1]!=0 || Buf[2] !=0 || Buf[3] !=1) return 0;//0x00000001?      else return 1;  }  while (!StartCodeFound){          if (feof (h264bitstream)){              nalu->len = (pos-1)-nalu->startcodeprefix_len;              memcpy (nalu->buf, &Buf[nalu->startcodeprefix_len], nalu->len);                   nalu->forbidden_bit = nalu->buf[0] & 0x80; //1 bit              nalu->nal_reference_idc = nalu->buf[0] & 0x60; // 2 bit              nalu->nal_unit_type = (nalu->buf[0]) & 0x1f;// 5 bit              free(Buf);              return pos-1;          }          Buf[pos++] = fgetc (h264bitstream);          info3 = FindStartCode3(&Buf[pos-4]);          if(info3 != 1)              info2 = FindStartCode2(&Buf[pos-3]);          StartCodeFound = (info2 == 1 || info3 == 1);      }  

解析：

 rewind = (info3 == 1)? -4 : -3;  fseek (h264bitstream, rewind, SEEK_CUR) nalu->len = (pos+rewind)-nalu->startcodeprefix_len;      memcpy (nalu->buf, &Buf[nalu->startcodeprefix_len], nalu->len);//      nalu->forbidden_bit = nalu->buf[0] & 0x80; //1 bit      nalu->nal_reference_idc = nalu->buf[0] & 0x60; // 2 bit      nalu->nal_unit_type = (nalu->buf[0]) & 0x1f;// 5 bit