一个基于JRTPLIB的轻量级RTSP客户端(myRTSPClient)——收流篇：（四）example代码解析

--------------------更新2018.08.20-------------------

添加http_tunnel_example.cpp作为RtspOverHttp示例程序。

--------------------更新2018.08.20结束-------------------

一、example逻辑伪码

myRTSPClient附带3个example程序：simple_example、complete_example、common_example。后两个example都是从simple_example中衍生出来的，以下将以simple_example为主进行解析，并且会在最后说明一下另两个example与simple_example的差别。

以下是simple_example简化后的伪代码，以便理解：

1. main():

2. 　　myRtspClient Client;

3. 　　Client.SetURI("rtsp://127.0.0.1/ansersion");

4. 　　Client.SendDESCRIBE();

5. 　　Client.SendSETUP();

6. 　　Client.SendPLAY();

7. 　　Write 1000 RTP Data to file "test_packet_recv.h264";

8. 　　Client.SendTEARDOWN();

9. 　　return;

二、simple_example.cpp代码注释

#include <iostream>
#include "rtspClient.h"
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

using std::cout;
using std::endl;

int main(int argc, char *argv[])
{
        string RtspUri("rtsp://127.0.0.1/ansersion");
        // string RtspUri("rtsp://192.168.81.145/ansersion");
        RtspClient Client;

        /* Set up rtsp server resource URI */
        Client.SetURI(RtspUri);

        /* Send DESCRIBE command to server */
        Client.DoDESCRIBE();

        /* Parse SDP message after sending DESCRIBE command */
        Client.ParseSDP(); // 解析RTSP服务端受理DESCRIBE命令后返回的SDP信息

        /* Send SETUP command to set up all 'audio' and 'video' 
         * sessions which SDP refers. */
        Client.DoSETUP();
        
        printf("start PLAY
");
        printf("SDP: %s
", Client.GetSDP().c_str());

        /* Send PLAY command to play only the 
         * 'video' sessions.*/
        Client.DoPLAY("video");

        /* Receive 1000 RTP 'video' packets
         * note(FIXME): 
         * if there are several 'video' session 
         * refered in SDP, only receive packets of the first 
         * 'video' session, the same as 'audio'.*/
        int packet_num = 0;
        uint8_t buf[65534];
        size_t size = 0;

        /* Write h264 video data to file "test_packet_recv.h264" 
         * Then it could be played by ffplay */
        int fd = open("test_packet_recv.h264", O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR | S_IXUSR);
        if(Client.GetSPSNalu(buf, &size)) { // 解码SDP中关于H264的SPS的数据
                if(write(fd, buf, size) < 0) { // 将SPS写入文件
                        perror("write");
                }
        } else {
                printf("SPS error
");
        }

        if(Client.GetPPSNalu(buf, &size)) { // 解码SDP中关于H264的PPS的数据
                if(write(fd, buf, size) < 0) { // 将PPS写入文件
                        perror("write");
                }
        } else {
                printf("PPS error
");
        }

        while(++packet_num < 1000) { // 接收1000个H264的数据包（确切的说是1000个NALU）
                if(!Client.GetMediaData("video", buf, &size)) continue;
                if(write(fd, buf, size) < 0) {
                        perror("write");
                }
                printf("recv %lu
", size);
        }

        printf("start TEARDOWN
");
        /* Send TEARDOWN command to teardown all of the sessions */
        Client.DoTEARDOWN();

        return 0;
}
                              

三、common_example.cpp和complete_example.cpp

common_example.cpp不同于simple_example.cpp的地方只有开头几行，这些代码是为了可以用参数指定RTSP URI。

int main(int argc, char *argv[])
{
        if(argc != 2) {
                cout << "Usage: " << argv[0] << " <URL>" << endl;
                cout << "For example: " << endl;
                cout << argv[0] << " rtsp://127.0.0.1/ansersion" << endl;
                return 1;
        }
        cout << "Start play " << argv[1] << endl;
        cout << "Then put video data into test_packet_recv.h264" << endl;
        string RtspUri(argv[1]);
        // string RtspUri("rtsp://192.168.81.145/ansersion");
        RtspClient Client;

        /* Set up rtsp server resource URI */
        Client.SetURI(RtspUri);
        ......
        return 0;
}

complete_example.cpp不同于simple_example.cpp的地方，就在于每次发送RTSP命令时， 它都会检查命令发送是否成功，并且检验返回信息是否是“200 OK”。

int main(int argc, char * argv[])
{
        ......      
         /* Send DESCRIBE command to server */
        if(Client.DoDESCRIBE() != RTSP_NO_ERROR) {
                printf("DoDESCRIBE error
");
                return 0;
        }
        printf("%s
", Client.GetResponse().c_str());
        /* Check whether server return '200'(OK) */
        if(!Client.IsResponse_200_OK()) {
                printf("DoDESCRIBE error
");
                return 0;
        }
        ......
        return 0;
}

OK！以上便是myRTSP的基础内容。

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