針對h264的解析網上優秀得博文、帖子一抓一大把，我就不在這班門弄斧了，僅僅提取一些自己在用的過程中比較有用的信息，對於sei自定義信息字段，雖然網上信息很多，但不容易精確搜到，就像我之前曾遇到一篇對我個人非常有用的文章，但后面一直找不到，現在再次看到，就把部分提取了出來，記錄下，方便自己后面再次用到方便，也看能不能幫助到部分碼友。
參考博客：https://www.jianshu.com/p/4d9120dfcd69
NAL header
起始碼（暗紅底色）"0x00000001"分割出來的比特流即是NAL unit，起始碼緊跟的第一個字節(墨綠底色)是NAL header。上圖“NAL header”一共出現了四個數值：
- "0x06"，此時NRI為"00B"，NAL unit type為SEI類型。
- “0x67”，此時NRI為“11B”，NAL unit type為SPS類型。
- “0x68”，此時NRI為“11B”，NAL unit type為PPS類型。
- “0x65”，此時NRI為“11B”，NAL unit type為IDR圖像。
SEI payload type
"0x06"后一個字節為“0x05”（淡黃底色）是SEI payload type，即表征SEI payload分析遵循user_data_unregistered()語法。
在國標中。sei payload type為5，為自定義消息：如圖
SEI payload size
“0x05”后一個字節為“0x2F”（淡藍底色）是SEI payload size，此時整個payload是47個字節。
SEI payload uuid
"0x2F"隨后的16個字節即為uuid，此時uuid為：
dc45e9bde6d948b7962cd820d923eeefSEI payload content
由於payload size是47個字節，除去16字節的uuid，剩下31個字節的content。由於content是字符串，所以有結束符"0x00"，有效的30個字符內容是
Zencoder Video Encoding System
rbsp trailing bits
47個payload字節后的"0x80"（灰底色）即是rbsp trailing bits，在user_data_unregistered()里面都是按字節寫入的，所以此時的NAL unit結尾寫入的字節一定是0x80。
下面開始解析一段含SEI信息的H264數據，數據中包含，坐標信息，人員信息，先把代碼貼出來，再一一說明代碼中的各個部分：
注：已經去除起始碼00 00 00 01了
可參考：https://blog.csdn.net/ab7936573/article/details/74135909
unsigned char* data_buf = NULL;
if ((data[0] & 0x1F) == 6)//判斷是否是SEI
{
int nCount = 0;
unsigned char buf[1602] = { 0 };
int nType = 0;
unsigned char * sei = (unsigned char *)(data + 1);
nCount = size;
//獲取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)//判斷為5，自定義消息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];
//解析人臉框坐標
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;
//解析人員信息
//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;
} //獲取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)//判斷為5，自定義消息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];
//解析人臉框坐標
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;
//解析人員信息
//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);
//數據長度
do {
sei_size += *sei;
} while (*sei++ == 255);
//檢查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;
}