RTP Header Parsing

< RTPHeader.h >

#ifndef __RTP_HEADER_H__
#define __RTP_HEADER_H__

typedef unsigned short      WORD;
typedef unsigned long       DWORD;

typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;

typedef unsigned int u_int32_t;
typedef unsigned short u_int16_t;
typedef unsigned char u_int8_t;

typedef struct
{
WORD    cc:     4;      /* csrc count */
WORD    ext:    1;      /* header extension flag */
WORD    pad:    1;      /* padding flag - for encryption */
WORD    ver:    2;      /* protocal version */
WORD    pt:     7;      /* payload type */
WORD    mk:     1;      /* marker bit - for profile */
WORD seq; /* sequence number of this packet */
DWORD ts; /* timestamp of this packet */
DWORD ssrc; /* source of packet */
} RTP_HEADER;

class RtpHeader {
public:
RtpHeader(uint8_t *buf, int len);
virtual ~RtpHeader();

uint8_t* payload();
int length() { return fLength; }
int payloadLen();

uint16_t version() { return fVersion; }
uint16_t padding() { return fPadding; }
uint16_t extension() { return fExtension; }
uint16_t csrcCount() { return fCSRCCount; }
uint16_t markerBit() { return fMarkerBit; }
uint16_t payloadType() { return fPayloadType; }
uint16_t sequenceNum() { return fSequenceNum; }
uint32_t timestamp() { return fTimestamp; }
uint32_t ssrc() { return fSSRC; }

private:
uint8_t* fBuf;
int fLength;
uint16_t fVersion;
uint16_t fPadding;
uint16_t fExtension;
uint16_t fCSRCCount;
uint16_t fMarkerBit;
uint16_t fPayloadType;
uint16_t fSequenceNum;
uint32_t fTimestamp;
uint32_t fSSRC;

uint8_t *fCurPtr;
};

#endif

< RTPHeader.cpp >

#include <Winsock2.h>
#include "RTPHeader.h"

RtpHeader::RtpHeader(uint8_t *buf, int len) : fBuf(NULL), fLength(0), fVersion(0), fPadding(0), fExtension(0), fCSRCCount(0),

fMarkerBit(0), fPayloadType(0), fSequenceNum(0), fTimestamp(0), fSSRC(0)

{

if (len < sizeof(RTP_HEADER))

return;

fBuf = fCurPtr = buf;

fLength = len;

RTP_HEADER *p = (RTP_HEADER *)buf;

fCSRCCount = p->cc;

fExtension = p->ext;

fPadding = p->pad;

fVersion = p->ver;

fPayloadType = p->pt;

fMarkerBit = p->mk;

fSequenceNum = ntohs(p->seq);

fTimestamp = ntohl(p->ts);

fSSRC = ntohl(p->ssrc);

fCurPtr += sizeof(RTP_HEADER);

// check RTP version (it must be 2)

if (fVersion != 2)

DPRINTF("invalid rtp version %u\n", fVersion);

// skip CSRC

if (fCSRCCount > 0) {

if (payloadLen() <= fCSRCCount*4) {

DPRINTF("invalid rtp header, CSRC count error %u\n", fCSRCCount);

} else {

fCurPtr += (fCSRCCount*4);

}

}

// skip Extension field

if (fExtension) {

if (payloadLen() <= 4) {

DPRINTF("invalid rtp header, extension length error\n");

} else {

unsigned extHdr = ntohl(*(unsigned *)fCurPtr); fCurPtr += 4;

unsigned remExtSize = 4*(extHdr&0xFFFF);

if (payloadLen() <= remExtSize) {

DPRINTF("invalid rtp header, extension size error %u\n", remExtSize);

} else {

fCurPtr += remExtSize;

}

}

}

// remove padding

if (fPadding) {

if (payloadLen() <= 0) {

DPRINTF("invalid rtp header, padding error\n");

} else {

unsigned numPaddingBytes = (unsigned)fBuf[fLength-1];

if (payloadLen() <= numPaddingBytes) {

DPRINTF("invalid rtp header, padding number error\n");

} else {

fLength -= numPaddingBytes;
    fPadding = p->pad = 0;

}

}

}

}

RtpHeader::~RtpHeader()

{

}

uint8_t* RtpHeader::payload()

{

return fCurPtr;

}

int RtpHeader::payloadLen()

{

uint8_t *ptrLast = &fBuf[fLength-1];

return ptrLast-fCurPtr+1;

}

< 사용 >

...

RtpHeader *rtp = new RtpHeader((uint8_t*)buf, len);

unsigned short pt = rtp->payloadType();

unsigned short mk = rtp->markerBit();

unsigned short seqnum = rtp->sequenceNum();

unsigned int ts = rtp->timestamp();

unsigned int rtpSSRC = rtp->ssrc();

 delete rtp;