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最近考虑使用RTP替换原有的高清视频传输协议，遂上网查找有关H264视频RTP打包、解包的文档和代码。功夫不负有心人，找到不少有价值的文档和代码。参考这些资料，写了H264 RTP打包类、解包类，实现了单个NAL单元包和FU_A分片单元包。对于丢包处理，采用简单的策略：丢弃随后的所有数据包，直到收到关键帧。测试效果还不错，代码贴上来，若能为同道中人借鉴一二，足矣。两个类的使用说明如下(省略了错误处理过程)：
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
// ...
}
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//
// 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)
{
}
//传入Set的数据必须是一个完整的NAL,起始码为0x00000001。
//起始码之前至少预留10个字节，以避免内存COPY操作。
//打包完成后，原缓冲区内的数据被破坏。
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 ;
}
//循环调用Get获取RTP包，直到返回值为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为H264 RTP视频数据包，nSize为RTP视频数据包字节长度，outSize为输出视频数据帧字节长度。
//返回值为指向视频数据帧的指针。输入数据可能被破坏。
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
{
// 码流正常
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
//
本文来自优快云博客，转载请标明出处：http://blog.youkuaiyun.com/dengzikun/archive/2010/08/12/5807694.aspx
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