H264码流中 分离和解析 nal

本文主要是介绍H264码流中 分离和解析 nal，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

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

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