h264解码之自定义信息（SEI）

     针对h264的解析网上优秀得博文、帖子一抓一大把，我就不在这班门弄斧了，仅仅提取一些自己在用的过程中比较有用的信息，对于sei自定义信息字段，虽然网上信息很多，但不容易精确搜到，就像我之前曾遇到一篇对我个人非常有用的文章，但后面一直找不到，现在再次看到，就把部分提取了出来，记录下，方便自己后面再次用到方便，也看能不能帮助到部分码友。

    参考博客：https://www.jianshu.com/p/4d9120dfcd69

NAL header

起始码（暗红底色）"0x00000001"分割出来的比特流即是NAL unit，起始码紧跟的第一个字节(墨绿底色)是NAL header。上图“NAL header”一共出现了四个数值：

• "0x06"，此时NRI为"00B"，NAL unit type为SEI类型。
• “0x67”，此时NRI为“11B”，NAL unit type为SPS类型。
• “0x68”，此时NRI为“11B”，NAL unit type为PPS类型。
• “0x65”，此时NRI为“11B”，NAL unit type为IDR图像。

SEI payload type

"0x06"后一个字节为“0x05”（淡黄底色）是SEI payload type，即表征SEI payload分析遵循user_data_unregistered()语法。

在国标中。sei payload type为5，为自定义消息：如图    

SEI payload size

“0x05”后一个字节为“0x2F”（淡蓝底色）是SEI payload size，此时整个payload是47个字节。

SEI payload uuid

"0x2F"随后的16个字节即为uuid，此时uuid为：

dc45e9bde6d948b7962cd820d923eeef

SEI payload content

由于payload size是47个字节，除去16字节的uuid，剩下31个字节的content。由于content是字符串，所以有结束符"0x00"，有效的30个字符内容是

Zencoder Video Encoding System

rbsp trailing bits

47个payload字节后的"0x80"（灰底色）即是rbsp trailing bits，在user_data_unregistered()里面都是按字节写入的，所以此时的NAL unit结尾写入的字节一定是0x80。

下面开始解析一段含SEI信息的H264数据，数据中包含，坐标信息，人员信息，先把代码贴出来，再一一说明代码中的各个部分：

注：已经去除起始码00 00 00 01了

可参考：https://blog.csdn.net/ab7936573/article/details/74135909

unsigned char* data_buf = NULL;
if ((data[0] & 0x1F) == 6)//判断是否是SEI
{
	int nCount = 0;

	unsigned char buf[1602] = { 0 };
	int nType = 0;
	unsigned char * sei = (unsigned char *)(data + 1);
	nCount = size;
        //获取SEI信息：payload size、payload type、uuid
	int nsize = get_sei_buffer(sei, ((unsigned char*)data + size - sei), buf, &nCount, &nType);
	if (5 == nType)//判断为5，自定义消息user_data_unregistered()
	{
		int nSd_Type = buf[0];

		if (1 == nSd_Type)
		{
			unsigned int nSd_Num = buf[1];
			m_nNumSize = nSd_Num;

			//max 100
			if (m_nNumSize > 100)
			{
				m_nNumSize = 100;
			}

			if (nSd_Num > 0)
			{
				for (int i = 0; i < m_nNumSize; i++)
				{
					BYTE buffer[8];
					//解析人脸框坐标
					buffer[0] = buf[i * 16 + 2];
					buffer[1] = buf[i * 16 + 3];
					unsigned short number = (buffer[0] << 8) + buffer[1];
					m_pFaceInfo[i].face_x = number;

					buffer[2] = buf[i * 16 + 4];
					buffer[3] = buf[i * 16 + 5];
					number = (buffer[2] << 8) + buffer[3];
					m_pFaceInfo[i].face_y = number;

					buffer[4] = buf[i * 16 + 6];
					buffer[5] = buf[i * 16 + 7];
					number = (buffer[4] << 8) + buffer[5];
					m_pFaceInfo[i].face_w = number;

					buffer[6] = buf[i * 16 + 8];
					buffer[7] = buf[i * 16 + 9];
					number = (buffer[6] << 8) + buffer[7];
					m_pFaceInfo[i].face_h = number;

					//解析人员信息
					//buffer[8] = *buf++;
					m_pFaceInfo[i].usrSex = buf[i * 16 + 10];
					m_pFaceInfo[i].userAge = buf[i * 16 + 11];
					m_pFaceInfo[i].userHairstyle = buf[i * 16 + 12];
					m_pFaceInfo[i].userHat = buf[i * 16 + 13];
					m_pFaceInfo[i].userBrow = buf[i * 16 + 16];
					m_pFaceInfo[i].userGlasses = buf[i * 16 + 14];
					m_pFaceInfo[i].userMask = buf[i * 16 + 17];
					m_pFaceInfo[i].userRace = buf[i * 16 + 18];
				}	
			}
		}
	}
	
	return;
}        //获取SEI信息：payload size、payload type、uuid
	int nsize = get_sei_buffer(sei, ((unsigned char*)data + size - sei), buf, &nCount, &nType);
	if (5 == nType)//判断为5，自定义消息user_data_unregistered()
	{
		int nSd_Type = buf[0];

		if (1 == nSd_Type)
		{
			unsigned int nSd_Num = buf[1];
			m_nNumSize = nSd_Num;

			//max 100
			if (m_nNumSize > 100)
			{
				m_nNumSize = 100;
			}

			if (nSd_Num > 0)
			{
				for (int i = 0; i < m_nNumSize; i++)
				{
					BYTE buffer[8];
					//解析人脸框坐标
					buffer[0] = buf[i * 16 + 2];
					buffer[1] = buf[i * 16 + 3];
					unsigned short number = (buffer[0] << 8) + buffer[1];
					m_pFaceInfo[i].face_x = number;

					buffer[2] = buf[i * 16 + 4];
					buffer[3] = buf[i * 16 + 5];
					number = (buffer[2] << 8) + buffer[3];
					m_pFaceInfo[i].face_y = number;

					buffer[4] = buf[i * 16 + 6];
					buffer[5] = buf[i * 16 + 7];
					number = (buffer[4] << 8) + buffer[5];
					m_pFaceInfo[i].face_w = number;

					buffer[6] = buf[i * 16 + 8];
					buffer[7] = buf[i * 16 + 9];
					number = (buffer[6] << 8) + buffer[7];
					m_pFaceInfo[i].face_h = number;

					//解析人员信息
					//buffer[8] = *buf++;
					m_pFaceInfo[i].usrSex = buf[i * 16 + 10];
					m_pFaceInfo[i].userAge = buf[i * 16 + 11];
					m_pFaceInfo[i].userHairstyle = buf[i * 16 + 12];
					m_pFaceInfo[i].userHat = buf[i * 16 + 13];
					m_pFaceInfo[i].userBrow = buf[i * 16 + 16];
					m_pFaceInfo[i].userGlasses = buf[i * 16 + 14];
					m_pFaceInfo[i].userMask = buf[i * 16 + 17];
					m_pFaceInfo[i].userRace = buf[i * 16 + 18];
				}	
			}
		}
	}
	
	return;
}

get_sei_buffer如下：

int get_sei_buffer(unsigned char * data, uint32_t size, unsigned char * buffer, int *count, int *nType)
{
	unsigned char * sei = data;
	int sei_type = 0;
	unsigned sei_size = 0;
	//payload type  
	do {
		sei_type += *sei;
		*nType = sei_type;
	} while (*sei++ == 255);
	//数据长度  
	do {
		sei_size += *sei;
	} while (*sei++ == 255);

	//检查UUID  
	static unsigned char uuid[] = { 0x73, 0x74, 0x64, 0x74, 0x73, 0x74, 0x64, 0x74, 0x73, 0x74, 0x64, 0x74, 0x73, 0x74, 0x64, 0x74 };

	if (sei_size >= UUID_SIZE && sei_size <= (data + size - sei) &&
		sei_type == 5 /*&& memcmp(sei, uuid, UUID_SIZE) == 0*/)
	{
		sei += UUID_SIZE;
		sei_size -= UUID_SIZE;

		if (buffer != NULL && count != NULL)
		{
			if (*count > (int)sei_size)
			{
				memcpy(buffer, sei, sei_size);
			}
		}

		*count = sei_size;

		return sei_size;
	}
	return -1;
}