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：
dc45e9bde6d948b7962cd820d923eeefSEI 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 Systemrbsp 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;
}