在应用层，很多时候 IDR、SEI、PPS、SPS 是打包在一起收到的， 需要手动解析出这几种帧类型。
定义 nalu 结构
typedef struct
{
uint32_t len; //! Length of the NAL unit (Excluding the start code, which does not belong to the NALU)
int32_t forbidden_bit; //! should be always FALSE
int32_t nal_reference_idc; //! NALU_PRIORITY_xxxx
int32_t nal_unit_type; //! NALU_TYPE_xxxx
char *buf; //! contains the first byte followed by the EBSP
} NALU_t;
从 Buffer 中查找 StartCode 0x0001 或 0x001， 并返回 StartCode 的长度
static int32_t FindStartCode(const char *buf)
{
if(buf[0] != 0x0 || buf[1] != 0x0 ){
return 0;
}
if(buf[2] == 0x1){
return 3;
} else if(buf[2] == 0x0){
if(buf[3] == 0x1){
return 4;
} else {
return 0;
}
} else {
return 0;
}
return 0;
}
从码流中读取完整的 nalu 信息存放在 NALU_t 结构中，返回本次读取到的 Nalu 长度
static int32_t ReadOneNaluFromBuf(const char *buffer, uint32_t nBufferSize, uint32_t offSet, NALU_t* pNalu)
{
uint32_t start = 0;
if( offSet < nBufferSize) {
start = FindStartCode(buffer + offSet);
if(start != 0) {
uint32_t pos = start;
while (offSet + pos < nBufferSize) {
if(buffer[offSet + pos++] == 0x00 &&
buffer[offSet + pos++] == 0x00 &&
buffer[offSet + pos++] == 0x00 &&
buffer[offSet + pos++] == 0x01
) {
break;
}
}
if(offSet + pos == nBufferSize){
pNalu->len = pos - start;
} else {
pNalu->len = (pos - 4) - start;
}
pNalu->buf =(char*)&buffer[offSet + start];
pNalu->forbidden_bit = pNalu->buf[0] & 0x80;
pNalu->nal_reference_idc = pNalu->buf[0] & 0x60; // 2 bit
pNalu->nal_unit_type = (pNalu->buf[0]) & 0x1f;// 5 bit
return (pNalu->len + start);
}
}
return 0;
}
循环读取，直到读完 buffer 中的所有 nalu
void parseH264(const char* pH264, uint32_t bufLen)
{
NALU_t nalu;
int32_t pos = 0, len = 0;
len = ReadOneNaluFromBuf(pH264, bufLen, pos, &nalu);
while (len != 0){
printf("## nalu type(%d)\n", nalu.nal_unit_type);
pos += len;
len = ReadOneNaluFromBuf(pH264, bufLen, pos, &nalu);
}
}