Question

RTP数据包由12字节RTP头和后续RTP有效载荷标题的第3和第4个字节包含最重要的字节和最不重要的字节 RTP数据包的序列号 Seq Num =（MSB <＆lt; 8）+ LSB

char pszPacket [12];

...

长lSeq = ???? - 如何从数据包中获取序列号？

Answer 1

unsigned short seq = (packet[2] << 8) | packet[3];

Answer 2

当然那只是“长lSeq =（unsigned char）（pszPacket [2]＆lt;＆lt; 8）|（unsigned char）pszPacket [3];”？

Answer 3

如果您需要适当的实现方式

typedef struct _RTPHeader
{
  //first byte
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
  unsigned int         CC:4;        /* CC field */
  unsigned int         X:1;         /* X field */
  unsigned int         P:1;         /* padding flag */
  unsigned int         version:2;
#elif G_BYTE_ORDER == G_BIG_ENDIAN
  unsigned int         version:2;
  unsigned int         P:1;         /* padding flag */
  unsigned int         X:1;         /* X field */
  unsigned int         CC:4;        /* CC field*/
#else
#error "G_BYTE_ORDER should be big or little endian."
#endif
  //second byte
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
  unsigned int         PT:7;     /* PT field */
  unsigned int         M:1;       /* M field */
#elif G_BYTE_ORDER == G_BIG_ENDIAN
  unsigned int         M:1;         /* M field */
  unsigned int         PT:7;       /* PT field */
#else
#error "G_BYTE_ORDER should be big or little endian."
#endif
  guint16              seq_num;      /* length of the recovery */
  guint32              TS;                   /* Timestamp */
  guint32              ssrc;
} RTPHeader; //12 bytes

您可以做的是：

char pszPacket[12];
RTPHeader* myRTPPacket = (RTPHeader*) pszPacket;
printf("Sequence number is: %hu", myRTPPacket->seq_num;

Answer 4

unsigned __int16 seq = _rotr16( *( unsigned __int16* )&packet[2] , 8 );

Answer 5

假设我们有一个指向字节缓冲区的指针，该缓冲区包含称为rtpBuffer的整个RTP数据包（包括RTP头），则可以使用以下代码提取位置2和3的16位字：

int8_t *rtpBuffer;

uint16_t packetSeqNbr = ntohs(*(reinterpret_cast<uint16_t *>(rtpBuffer + 2)));

ntohs（）用于从网络字节顺序转换为主机字节顺序，以便代码可移植到不同的机器上。

RTP序列提取物

5 个答案: