最近考慮使用RTP替換原有的高清視訊傳輸協議，遂上網查詢有關H264視訊RTP打包、解包的文件和程式碼。功夫不負有心人，找到不少有價值的文件和程式碼。參考這些資料，寫了H264 RTP打包類、解包類，實現了單個NAL單元包和FU_A分片單元包。對於丟包處理，採用簡單的策略：丟棄隨後的所有資料包，直到收到關鍵幀。測試效果還不錯，程式碼貼上來，若能為同道中人借鑑一二，足矣。兩個類的使用說明如下(省略了錯誤處理過程)：

 DWORD H264SSRC ;
 CH264_RTP_PACK pack ( H264SSRC ) ;
 BYTE *pVideoData ;
 DWORD Size, ts ;
 bool IsEndOfFrame ;
 WORD wLen ;
 pack.Set ( pVideoData, Size, ts, IsEndOfFrame ) ;
 BYTE *pPacket ;
 while ( pPacket = pack.Get ( &wLen ) )
 {
  // rtp packet process
  // ...
 }

 HRESULT hr ;
 CH264_RTP_UNPACK unpack ( hr ) ;
 BYTE *pRtpData ;
 WORD inSize;
 int outSize ;
 BYTE *pFrame = unpack.Parse_RTP_Packet ( pRtpData, inSize, &outSize ) ;
 if ( pFrame != NULL )
 {
  // frame process
  // ...
 }

 ////////////////////////////////////////////////////////////////////////////////////////// // class CH264_RTP_PACK start class CH264_RTP_PACK { #define RTP_VERSION 2 typedef struct NAL_msg_s { bool eoFrame ; unsigned char type; // NAL type unsigned char *start; // pointer to first location in the send buffer unsigned char *end; // pointer to last location in send buffer unsigned long size ; } NAL_MSG_t; typedef struct { //LITTLE_ENDIAN unsigned short cc:4; /* CSRC count */ unsigned short x:1; /* header extension flag */ unsigned short p:1; /* padding flag */ unsigned short v:2; /* packet type */ unsigned short pt:7; /* payload type */ unsigned short m:1; /* marker bit */ unsigned short seq; /* sequence number */ unsigned long ts; /* timestamp */ unsigned long ssrc; /* synchronization source */ } rtp_hdr_t; typedef struct tagRTP_INFO { NAL_MSG_t nal; // NAL information rtp_hdr_t rtp_hdr; // RTP header is assembled here int hdr_len; // length of RTP header unsigned char *pRTP; // pointer to where RTP packet has beem assembled unsigned char *start; // pointer to start of payload unsigned char *end; // pointer to end of payload unsigned int s_bit; // bit in the FU header unsigned int e_bit; // bit in the FU header bool FU_flag; // fragmented NAL Unit flag } RTP_INFO; public: CH264_RTP_PACK(unsigned long H264SSRC, unsigned char H264PAYLOADTYPE=96, unsigned short MAXRTPPACKSIZE=1472 ) { m_MAXRTPPACKSIZE = MAXRTPPACKSIZE ; if ( m_MAXRTPPACKSIZE > 10000 ) { m_MAXRTPPACKSIZE = 10000 ; } if ( m_MAXRTPPACKSIZE < 50 ) { m_MAXRTPPACKSIZE = 50 ; } memset ( &m_RTP_Info, 0, sizeof(m_RTP_Info) ) ; m_RTP_Info.rtp_hdr.pt = H264PAYLOADTYPE ; m_RTP_Info.rtp_hdr.ssrc = H264SSRC ; m_RTP_Info.rtp_hdr.v = RTP_VERSION ; m_RTP_Info.rtp_hdr.seq = 0 ; } ~CH264_RTP_PACK(void) { } //傳入Set的資料必須是一個完整的NAL,起始碼為0x00000001。 //起始碼之前至少預留10個位元組，以避免記憶體COPY操作。 //打包完成後，原緩衝區內的資料被破壞。 bool Set ( unsigned char *NAL_Buf, unsigned long NAL_Size, unsigned long Time_Stamp, bool End_Of_Frame ) { unsigned long startcode = StartCode(NAL_Buf) ; if ( startcode != 0x01000000 ) { return false ; } int type = NAL_Buf[4] & 0x1f ; if ( type < 1 || type > 12 ) { return false ; } m_RTP_Info.nal.start = NAL_Buf ; m_RTP_Info.nal.size = NAL_Size ; m_RTP_Info.nal.eoFrame = End_Of_Frame ; m_RTP_Info.nal.type = m_RTP_Info.nal.start[4] ; m_RTP_Info.nal.end = m_RTP_Info.nal.start + m_RTP_Info.nal.size ; m_RTP_Info.rtp_hdr.ts = Time_Stamp ; m_RTP_Info.nal.start += 4 ; // skip the syncword if ( (m_RTP_Info.nal.size + 7) > m_MAXRTPPACKSIZE ) { m_RTP_Info.FU_flag = true ; m_RTP_Info.s_bit = 1 ; m_RTP_Info.e_bit = 0 ; m_RTP_Info.nal.start += 1 ; // skip NAL header } else { m_RTP_Info.FU_flag = false ; m_RTP_Info.s_bit = m_RTP_Info.e_bit = 0 ; } m_RTP_Info.start = m_RTP_Info.end = m_RTP_Info.nal.start ; m_bBeginNAL = true ; return true ; } //迴圈呼叫Get獲取RTP包，直到返回值為NULL unsigned char* Get ( unsigned short *pPacketSize ) { if ( m_RTP_Info.end == m_RTP_Info.nal.end ) { *pPacketSize = 0 ; return NULL ; } if ( m_bBeginNAL ) { m_bBeginNAL = false ; } else { m_RTP_Info.start = m_RTP_Info.end; // continue with the next RTP-FU packet } int bytesLeft = m_RTP_Info.nal.end - m_RTP_Info.start ; int maxSize = m_MAXRTPPACKSIZE - 12 ; // sizeof(basic rtp header) == 12 bytes if ( m_RTP_Info.FU_flag ) maxSize -= 2 ; if ( bytesLeft > maxSize ) { m_RTP_Info.end = m_RTP_Info.start + maxSize ; // limit RTP packetsize to 1472 bytes } else { m_RTP_Info.end = m_RTP_Info.start + bytesLeft ; } if ( m_RTP_Info.FU_flag ) { // multiple packet NAL slice if ( m_RTP_Info.end == m_RTP_Info.nal.end ) { m_RTP_Info.e_bit = 1 ; } } m_RTP_Info.rtp_hdr.m = m_RTP_Info.nal.eoFrame ? 1 : 0 ; // should be set at EofFrame if ( m_RTP_Info.FU_flag && !m_RTP_Info.e_bit ) { m_RTP_Info.rtp_hdr.m = 0 ; } m_RTP_Info.rtp_hdr.seq++ ; unsigned char *cp = m_RTP_Info.start ; cp -= ( m_RTP_Info.FU_flag ? 14 : 12 ) ; m_RTP_Info.pRTP = cp ; unsigned char *cp2 = (unsigned char *)&m_RTP_Info.rtp_hdr ; cp[0] = cp2[0] ; cp[1] = cp2[1] ; cp[2] = ( m_RTP_Info.rtp_hdr.seq >> 8 ) & 0xff ; cp[3] = m_RTP_Info.rtp_hdr.seq & 0xff ; cp[4] = ( m_RTP_Info.rtp_hdr.ts >> 24 ) & 0xff ; cp[5] = ( m_RTP_Info.rtp_hdr.ts >> 16 ) & 0xff ; cp[6] = ( m_RTP_Info.rtp_hdr.ts >> 8 ) & 0xff ; cp[7] = m_RTP_Info.rtp_hdr.ts & 0xff ; cp[8] = ( m_RTP_Info.rtp_hdr.ssrc >> 24 ) & 0xff ; cp[9] = ( m_RTP_Info.rtp_hdr.ssrc >> 16 ) & 0xff ; cp[10] = ( m_RTP_Info.rtp_hdr.ssrc >> 8 ) & 0xff ; cp[11] = m_RTP_Info.rtp_hdr.ssrc & 0xff ; m_RTP_Info.hdr_len = 12 ; /*! * /n The FU indicator octet has the following format: * /n * /n +---------------+ * /n MSB |0|1|2|3|4|5|6|7| LSB * /n +-+-+-+-+-+-+-+-+ * /n |F|NRI| Type | * /n +---------------+ * /n * /n The FU header has the following format: * /n * /n +---------------+ * /n |0|1|2|3|4|5|6|7| * /n +-+-+-+-+-+-+-+-+ * /n |S|E|R| Type | * /n +---------------+ */ if ( m_RTP_Info.FU_flag ) { // FU indicator F|NRI|Type cp[12] = ( m_RTP_Info.nal.type & 0xe0 ) | 28 ; //Type is 28 for FU_A //FU header S|E|R|Type cp[13] = ( m_RTP_Info.s_bit << 7 ) | ( m_RTP_Info.e_bit << 6 ) | ( m_RTP_Info.nal.type & 0x1f ) ; //R = 0, must be ignored by receiver m_RTP_Info.s_bit = m_RTP_Info.e_bit= 0 ; m_RTP_Info.hdr_len = 14 ; } m_RTP_Info.start = &cp[m_RTP_Info.hdr_len] ; // new start of payload *pPacketSize = m_RTP_Info.hdr_len + ( m_RTP_Info.end - m_RTP_Info.start ) ; return m_RTP_Info.pRTP ; } private: unsigned int StartCode( unsigned char *cp ) { unsigned int d32 ; d32 = cp[3] ; d32 <<= 8 ; d32 |= cp[2] ; d32 <<= 8 ; d32 |= cp[1] ; d32 <<= 8 ; d32 |= cp[0] ; return d32 ; } private: RTP_INFO m_RTP_Info ; bool m_bBeginNAL ; unsigned short m_MAXRTPPACKSIZE ; }; // class CH264_RTP_PACK end ////////////////////////////////////////////////////////////////////////////////////////// ////////////////////////////////////////////////////////////////////////////////////////// // class CH264_RTP_UNPACK start class CH264_RTP_UNPACK { #define RTP_VERSION 2 #define BUF_SIZE (1024 * 500) typedef struct { //LITTLE_ENDIAN unsigned short cc:4; /* CSRC count */ unsigned short x:1; /* header extension flag */ unsigned short p:1; /* padding flag */ unsigned short v:2; /* packet type */ unsigned short pt:7; /* payload type */ unsigned short m:1; /* marker bit */ unsigned short seq; /* sequence number */ unsigned long ts; /* timestamp */ unsigned long ssrc; /* synchronization source */ } rtp_hdr_t; public: CH264_RTP_UNPACK ( HRESULT &hr, unsigned char H264PAYLOADTYPE = 96 ) : m_bSPSFound(false) , m_bWaitKeyFrame(true) , m_bPrevFrameEnd(false) , m_bAssemblingFrame(false) , m_wSeq(1234) , m_ssrc(0) { m_pBuf = new BYTE[BUF_SIZE] ; if ( m_pBuf == NULL ) { hr = E_OUTOFMEMORY ; return ; } m_H264PAYLOADTYPE = H264PAYLOADTYPE ; m_pEnd = m_pBuf + BUF_SIZE ; m_pStart = m_pBuf ; m_dwSize = 0 ; hr = S_OK ; } ~CH264_RTP_UNPACK(void) { delete [] m_pBuf ; } //pBuf為H264 RTP視訊資料包，nSize為RTP視訊資料包位元組長度，outSize為輸出視訊資料幀位元組長度。 //返回值為指向視訊資料幀的指標。輸入資料可能被破壞。 BYTE* Parse_RTP_Packet ( BYTE *pBuf, unsigned short nSize, int *outSize ) { if ( nSize <= 12 ) { return NULL ; } BYTE *cp = (BYTE*)&m_RTP_Header ; cp[0] = pBuf[0] ; cp[1] = pBuf[1] ; m_RTP_Header.seq = pBuf[2] ; m_RTP_Header.seq <<= 8 ; m_RTP_Header.seq |= pBuf[3] ; m_RTP_Header.ts = pBuf[4] ; m_RTP_Header.ts <<= 8 ; m_RTP_Header.ts |= pBuf[5] ; m_RTP_Header.ts <<= 8 ; m_RTP_Header.ts |= pBuf[6] ; m_RTP_Header.ts <<= 8 ; m_RTP_Header.ts |= pBuf[7] ; m_RTP_Header.ssrc = pBuf[8] ; m_RTP_Header.ssrc <<= 8 ; m_RTP_Header.ssrc |= pBuf[9] ; m_RTP_Header.ssrc <<= 8 ; m_RTP_Header.ssrc |= pBuf[10] ; m_RTP_Header.ssrc <<= 8 ; m_RTP_Header.ssrc |= pBuf[11] ; BYTE *pPayload = pBuf + 12 ; DWORD PayloadSize = nSize - 12 ; // Check the RTP version number (it should be 2): if ( m_RTP_Header.v != RTP_VERSION ) { return NULL ; } /* // Skip over any CSRC identifiers in the header: if ( m_RTP_Header.cc ) { long cc = m_RTP_Header.cc * 4 ; if ( Size < cc ) { return NULL ; } Size -= cc ; p += cc ; } // Check for (& ignore) any RTP header extension if ( m_RTP_Header.x ) { if ( Size < 4 ) { return NULL ; } Size -= 4 ; p += 2 ; long l = p[0] ; l <<= 8 ; l |= p[1] ; p += 2 ; l *= 4 ; if ( Size < l ) ; { return NULL ; } Size -= l ; p += l ; } // Discard any padding bytes: if ( m_RTP_Header.p ) { if ( Size == 0 ) { return NULL ; } long Padding = p[Size-1] ; if ( Size < Padding ) { return NULL ; } Size -= Padding ; }*/ // Check the Payload Type. if ( m_RTP_Header.pt != m_H264PAYLOADTYPE ) { return NULL ; } int PayloadType = pPayload[0] & 0x1f ; int NALType = PayloadType ; if ( NALType == 28 ) // FU_A { if ( PayloadSize < 2 ) { return NULL ; } NALType = pPayload[1] & 0x1f ; } if ( m_ssrc != m_RTP_Header.ssrc ) { m_ssrc = m_RTP_Header.ssrc ; SetLostPacket () ; } if ( NALType == 0x07 ) // SPS { m_bSPSFound = true ; } if ( !m_bSPSFound ) { return NULL ; } if ( NALType == 0x07 || NALType == 0x08 ) // SPS PPS { m_wSeq = m_RTP_Header.seq ; m_bPrevFrameEnd = true ; pPayload -= 4 ; *((DWORD*)(pPayload)) = 0x01000000 ; *outSize = PayloadSize + 4 ; return pPayload ; } if ( m_bWaitKeyFrame ) { if ( m_RTP_Header.m ) // frame end { m_bPrevFrameEnd = true ; if ( !m_bAssemblingFrame ) { m_wSeq = m_RTP_Header.seq ; return NULL ; } } if ( !m_bPrevFrameEnd ) { m_wSeq = m_RTP_Header.seq ; return NULL ; } else { if ( NALType != 0x05 ) // KEY FRAME { m_wSeq = m_RTP_Header.seq ; m_bPrevFrameEnd = false ; return NULL ; } } } /////////////////////////////////////////////////////////////// if ( m_RTP_Header.seq != (WORD)( m_wSeq + 1 ) ) // lost packet { m_wSeq = m_RTP_Header.seq ; SetLostPacket () ; return NULL ; } else { // 碼流正常 m_wSeq = m_RTP_Header.seq ; m_bAssemblingFrame = true ; if ( PayloadType != 28 ) // whole NAL { *((DWORD*)(m_pStart)) = 0x01000000 ; m_pStart += 4 ; m_dwSize += 4 ; } else // FU_A { if ( pPayload[1] & 0x80 ) // FU_A start { *((DWORD*)(m_pStart)) = 0x01000000 ; m_pStart += 4 ; m_dwSize += 4 ; pPayload[1] = ( pPayload[0] & 0xE0 ) | NALType ; pPayload += 1 ; PayloadSize -= 1 ; } else { pPayload += 2 ; PayloadSize -= 2 ; } } if ( m_pStart + PayloadSize < m_pEnd ) { CopyMemory ( m_pStart, pPayload, PayloadSize ) ; m_dwSize += PayloadSize ; m_pStart += PayloadSize ; } else // memory overflow { SetLostPacket () ; return NULL ; } if ( m_RTP_Header.m ) // frame end { *outSize = m_dwSize ; m_pStart = m_pBuf ; m_dwSize = 0 ; if ( NALType == 0x05 ) // KEY FRAME { m_bWaitKeyFrame = false ; } return m_pBuf ; } else { return NULL ; } } } void SetLostPacket() { m_bSPSFound = false ; m_bWaitKeyFrame = true ; m_bPrevFrameEnd = false ; m_bAssemblingFrame = false ; m_pStart = m_pBuf ; m_dwSize = 0 ; } private: rtp_hdr_t m_RTP_Header ; BYTE *m_pBuf ; bool m_bSPSFound ; bool m_bWaitKeyFrame ; bool m_bAssemblingFrame ; bool m_bPrevFrameEnd ; BYTE *m_pStart ; BYTE *m_pEnd ; DWORD m_dwSize ; WORD m_wSeq ; BYTE m_H264PAYLOADTYPE ; DWORD m_ssrc ; }; // class CH264_RTP_UNPACK end //////////////////////////////////////////////////////////////////////////////////////////