Packet mode and three streaming modes in SDP protocol

1、rtsp Medium sdp agreement

sdp The name is Session Description Protocol , Include sip This is also used in the agreement
rtsp The protocol can transmit ps flow ,ts flow , Bare flow is also called es flow ,es The flow is more conventional , be familiar with h264 Of rtp The way the packet is packaged , perhaps h265 The way the packet is packaged ,h265 Packet RTP You can refer to ffmpeg Source code
rtsp Agreement If the transmission is h264 h265
“m=” The media name in the line is “video”
“a=rtpmap” The code name in the line is H264 h265
“a=rtpmap” The clock frequency in the row is generally 90000, It can be other numbers , however 90000 This number is suitable for many frame rates , So use it .
Other parameters are included in “a=fmtp” .

2、pm The way

packetization-mode:
Indicates the supported packet mode .
1 、packetization-mode The value is 0 Or when it doesn't exist , A single... Must be used NALU Unit mode .
2、 packetization-mode The value is 1 Use non interlaced (non-interleaved) Packet mode .
3、 packetization-mode The value is 2 Use interleaving (interleaved) Packet mode .

profile-level-id:
This parameter is used to indicate H.264 The flow of profile Type and level . from Base16( Hexadecimal ) It means 3 Bytes . The first byte indicates H.264 Of Profile type , The third byte represents H.264 Of Profile Level

We usually use packetization-mode = 1, Non staggered mode

3、ps 、ts、es transmission mode

The following code is used to recover rtsp The scenario transmits three different streams

int handle_cmd(string& cmd, string& CSeq, uint32_t sessionid, char* cmdres,int ps_n_ts)
	{
    
		#define BUFSIZE 8*1024

		int h26xtype = 96;
		if (cmd.compare("DESCRIBE") == 0)
		{
    
			const char * psnts;
			if (ps_n_ts == 1)
			{
    
				psnts = "a=rtpmap:32 MP2P/90000";
				h26xtype = 32;
			}
			else if (ps_n_ts == 2)
			{
    
				psnts = "a=rtpmap:96 H264/90000";
				h26xtype = 96;
			}
			else if (ps_n_ts == 3)
			{
    
				psnts = "a=rtpmap:33 MP2T/90000";
				h26xtype = 33;
			}
			char sdp[4096];
			sprintf(sdp, "v=0\r\n"
				"o=shyjx 22345 22345 IN IP4 %s\r\n"
				"s=H.264 Video, streamed by qb\r\n"
				"t=0 0\r\n"
				//"m=video 0 RTP/AVP 96\r\n"
				"%s\r\n"
				"c=IN IP4 0.0.0.0\r\n"
				"a=rtpmap:96 H264/90000\r\n"
				"a=fmtp:96 packetization-mode=1;\r\n"
				"a=control:stream", m_strlocalip.c_str(), psnts, h26xtype);
			return buildDescribeRes(cmdres, BUFSIZE, sdp, CSeq.c_str());
		}
		else if (cmd.compare("OPTIONS") == 0)
		{
    
			return buildOptionRes(cmdres, BUFSIZE, CSeq.c_str());
		}
		else if (cmd.compare("SETUP") == 0)
		{
    
			return buildSetupTcpRes(cmdres, BUFSIZE, 0, 1, sessionid, CSeq.c_str());
		}
		else if (cmd.compare("PLAY") == 0)
		{
    
			return buildPlayRes(cmdres, BUFSIZE, NULL, sessionid, CSeq.c_str());
		}
		else if (cmd.compare("TEARDOWN") == 0)
		{
    
			return buildTeardownRes(cmdres, BUFSIZE, sessionid, CSeq.c_str());
		}
		return -1;
	}