从零开始写一个RTSP服务器（七）多播传输RTP包

秒速五厘米 2021-11-01 23:40 443阅读 0赞

**从零开始写一个RTSP服务器系列**

[★我的开源项目-RtspServer][-RtspServer]

[从零开始写一个RTSP服务器（一）RTSP协议讲解][RTSP_RTSP]

[从零开始写一个RTSP服务器（二）RTSP协议的实现][RTSP_RTSP 1]

[从零开始写一个RTSP服务器（三）RTP传输H.264][RTSP_RTP_H.264]

[从零开始写一个RTSP服务器（四）一个传输H.264的RTSP服务器][RTSP_H.264_RTSP]

[从零开始写一个RTSP服务器（五）RTP传输AAC][RTSP_RTP_AAC]

[从零开始写一个RTSP服务器（六）一个传输AAC的RTSP服务器][RTSP_AAC_RTSP]

[从零开始写一个RTSP服务器（七）多播传输RTP包][RTSP_RTP]

[从零开始写一个RTSP服务器（八）一个多播的RTSP服务器][RTSP_RTSP 2]

[从零开始写一个RTSP服务器（九）一个RTP OVER RTSP/TCP的RTSP服务器][RTSP_RTP OVER RTSP_TCP_RTSP]

# 从零开始写一个RTSP服务器（七）多播传输RTP包 #

### 文章目录 ###

*  从零开始写一个RTSP服务器（七）多播传输RTP包
 *   *  一、多播
     *   *  1.1 多播简介
         *  1.2 多播示例
     *  二、多播的sdp描述文件
     *  三、多播传输RTP包实现
     *   *  3.1 实现
         *  3.2 源码
         *   *  multicast.c
             *  rtp.h
             *  rtp.c
     *  四、测试

## 一、多播 ##

### 1.1 多播简介 ###

单播地址标识当个IP接口，广播地址标识某个子网的所有IP接口，多播地址标识一组IP接口

单播和多播是两个极端，多播则在这两者之间折衷

多播数据报只由加入多播组的应用的主机的接口接收

IPV4的D类地址是IPV4的多播地址，范围是（224.0.0.0-239.255.255.255）

下面这张图对多播地址进行细分

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjQ2MjIwMg_size_16_color_FFFFFF_t_70]

### 1.2 多播示例 ###

下面讲解一下多播的客户端与服务端编程

*  服务端
    
    多播服务端并不需要什么特殊的操作，只需要创建udp套接字，然后向多播地址指定端口发送数据就行
 *  客户端
    
    多播客户端需要做的工作是，创建udp套接字，绑定多播端口，加入多播组

下面是示例代码

*  服务端
    
        /*
        *broadcast_server.c - 多播服务程序
        */
        #include <sys/types.h>    
        #include <sys/socket.h>    
        #include <netinet/in.h>    
        #include <arpa/inet.h>    
        #include <time.h>    
        #include <string.h>    
        #include <stdio.h>    
        #include <unistd.h>    
        #include <stdlib.h>
        
        #define MCAST_PORT 8888
        #define MCAST_ADDR "239.255.255.11"
        #define MCAST_DATA "BROADCAST TEST DATA"            /*多播发送的数据*/
        #define MCAST_INTERVAL 1                            /*发送间隔时间*/
        
        int main(int argc, char*argv)
        {
              
            struct sockaddr_in mcast_addr;     
            int fd = socket(AF_INET, SOCK_DGRAM, 0);         /*建立套接字*/
            if (fd == -1)
            {
              
                perror("socket()");
                exit(1);
            }
           
            memset(&mcast_addr, 0, sizeof(mcast_addr));/*初始化IP多播地址为0*/
            mcast_addr.sin_family = AF_INET;                /*设置协议族类行为AF*/
            mcast_addr.sin_addr.s_addr = inet_addr(MCAST_ADDR);/*设置多播IP地址*/
            mcast_addr.sin_port = htons(MCAST_PORT);        /*设置多播端口*/
           
            /*向多播地址发送数据*/
            while(1) 
            {
              
                int n = sendto(fd,MCAST_DATA,sizeof(MCAST_DATA),0,(struct sockaddr*)&mcast_addr,sizeof(mcast_addr)) ;
                if( n < 0)
                {
              
                    perror("sendto()");
                    exit(1);
                }      
                sleep(MCAST_INTERVAL);                          /*等待一段时间*/
            }
           
            return 0;
        }
 *  客户端
    
        /*
        *broadcast_client.c - 多播的客户端
        */
        #include <sys/types.h>    
        #include <sys/socket.h>    
        #include <netinet/in.h>    
        #include <arpa/inet.h>    
        #include <time.h>    
        #include <string.h>    
        #include <stdio.h>    
        #include <unistd.h>    
        #include <stdlib.h>
        
        #define MCAST_PORT 8888
        #define MCAST_ADDR "239.255.255.11"
        #define MCAST_INTERVAL 1             /*发送间隔时间*/
        #define BUFF_SIZE 256                /*接收缓冲区大小*/
        
        int main(int argc, char*argv[])
        {
                
            struct sockaddr_in local_addr;              /*本地地址*/
           
            int fd = socket(AF_INET, SOCK_DGRAM, 0);     /*建立套接字*/
            if (fd == -1)
            {
              
                perror("socket()");
                exit(1);
            }  
            
            int yes = 1;
            if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(yes)) < 0)     
            {
                  
                perror("Reusing ADDR failed");    
                exit(1);    
            }
           
            /*初始化本地地址*/
            memset(&local_addr, 0, sizeof(local_addr));
            local_addr.sin_family = AF_INET;
            local_addr.sin_addr.s_addr = htonl(INADDR_ANY);
            local_addr.sin_port = htons(MCAST_PORT);
        
            /*绑定socket*/
            int err = bind(fd,(struct sockaddr*)&local_addr, sizeof(local_addr)) ;
            if(err < 0)
            {
              
                perror("bind()");
                exit(1);
            }
           
            /*设置回环许可*/
            int loop = 1;
            err = setsockopt(fd,IPPROTO_IP, IP_MULTICAST_LOOP,&loop, sizeof(loop));
            if(err < 0)
            {
              
                perror("setsockopt():IP_MULTICAST_LOOP");
                exit(1);
            }
           
            /*加入多播组*/
            struct ip_mreq mreq;                                    
            mreq.imr_multiaddr.s_addr = inet_addr(MCAST_ADDR); /*多播地址*/
            mreq.imr_interface.s_addr = htonl(INADDR_ANY); /*本地网络接口为默认*/
            
            /*将本机加入多播组*/
            err = setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP,&mreq, sizeof(mreq));
            if (err < 0)
            {
              
                perror("setsockopt():IP_ADD_MEMBERSHIP");
                exit(1);
            }
           
            int times = 0;
            int addr_len = sizeof(local_addr);
            char buff[BUFF_SIZE];
            int n = 0;
            
            /*循环接收多播组的消息，5次后退出*/
            for(times = 0;times < 5;times++)
            {
              
                memset(buff, 0, BUFF_SIZE);                 /*清空接收缓冲区*/
                
                /*接收数据*/
                n = recvfrom(fd, buff, BUFF_SIZE, 0,(struct sockaddr*)&local_addr,&addr_len);
                if( n== -1)
                {
              
                    perror("recvfrom()");
                }
                                                            /*打印信息*/
                printf("Recv %dst message from server:%s\n", times, buff);
                sleep(MCAST_INTERVAL);
            }
           
            /*退出多播组*/
            err = setsockopt(fd, IPPROTO_IP, IP_DROP_MEMBERSHIP,&mreq, sizeof(mreq));
               
            close(fd);
            return 0;
        }

需要好好看一看这个示例，了解多播编程的流程

## 二、多播的sdp描述文件 ##

m=video 9832 RTP/AVP 96
    c=IN IP4 239.255.255.11/255
    a=rtpmap:96 H264/90000
    a=framerate:25

这是一个多播H.264的sdp文件

相关的讲解前面已经讲了很多了（详情看：[从零开始写一个RTSP服务器（一）不一样的RTSP协议讲解][RTSP_RTSP]）

这里需要注意的是目的端口号为`9832`，多播IP为`239.255.255.11`

## 三、多播传输RTP包实现 ##

### 3.1 实现 ###

对于我们来说，我们实现的是服务端，所以非常简单，无需过多操作，只需要把[从零开始写一个RTSP服务器（三）RTP传输H.264][RTSP_RTP_H.264]中的目的IP和目的端口改为目的多播IP和目的多播端口就行

关于RTP打包这里不再重复，前面已经讲解得非常详细了

### 3.2 源码 ###

#### multicast.c ####

/*
     * 作者：_JT_
     * 博客：https://blog.csdn.net/weixin_42462202
     */
    
    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    #include <unistd.h>
    #include <string.h>
    
    #include "rtp.h"
    
    #define H264_FILE_NAME      "test.h264"
    #define MULTICAST_IP        "239.255.255.11"
    #define MULTICAST_PORT      9832
    #define FPS                 25
    
    static inline int startCode3(char* buf)
    {
        
        if(buf[0] == 0 && buf[1] == 0 && buf[2] == 1)
            return 1;
        else
            return 0;
    }
    
    static inline int startCode4(char* buf)
    {
        
        if(buf[0] == 0 && buf[1] == 0 && buf[2] == 0 && buf[3] == 1)
            return 1;
        else
            return 0;
    }
    
    static char* findNextStartCode(char* buf, int len)
    {
        
        int i;
    
        if(len < 3)
            return NULL;
    
        for(i = 0; i < len-3; ++i)
        {
        
            if(startCode3(buf) || startCode4(buf))
                return buf;
            
            ++buf;
        }
    
        if(startCode3(buf))
            return buf;
    
        return NULL;
    }
    
    static int getFrameFromH264File(int fd, char* frame, int size)
    {
        
        int rSize, frameSize;
        char* nextStartCode;
    
        if(fd < 0)
            return fd;
    
        rSize = read(fd, frame, size);
        if(!startCode3(frame) && !startCode4(frame))
            return -1;
        
        nextStartCode = findNextStartCode(frame+3, rSize-3);
        if(!nextStartCode)
        {
        
            lseek(fd, 0, SEEK_SET);
            frameSize = rSize;
        }
        else
        {
        
            frameSize = (nextStartCode-frame);
            lseek(fd, frameSize-rSize, SEEK_CUR);
        }
    
        return frameSize;
    }
    
    static int createUdpSocket()
    {
        
        int fd;
        int on = 1;
    
        fd = socket(AF_INET, SOCK_DGRAM, 0);
        if(fd < 0)
            return -1;
    
        setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (const char*)&on, sizeof(on));
    
        return fd;
    }
    
    static int rtpSendH264Frame(int socket, char* ip, int16_t port,
                                struct RtpPacket* rtpPacket, uint8_t* frame, uint32_t frameSize)
    {
        
        uint8_t naluType; // nalu第一个字节
        int sendBytes = 0;
        int ret;
    
        naluType = frame[0];
    
        if (frameSize <= RTP_MAX_PKT_SIZE) // nalu长度小于最大包场：单一NALU单元模式
        {
        
            /*
             *   0 1 2 3 4 5 6 7 8 9
             *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             *  |F|NRI|  Type   | a single NAL unit ... |
             *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             */
            memcpy(rtpPacket->payload, frame, frameSize);
            ret = rtpSendPacket(socket, ip, port, rtpPacket, frameSize);
            if(ret < 0)
                return -1;
    
            rtpPacket->rtpHeader.seq++;
            sendBytes += ret;
            if ((naluType & 0x1F) == 7 || (naluType & 0x1F) == 8) // 如果是SPS、PPS就不需要加时间戳
                goto out;
        }
        else // nalu长度小于最大包场：分片模式
        {
        
            /*
             *  0                   1                   2
             *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
             * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             * | FU indicator  |   FU header   |   FU payload   ...  |
             * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             */
    
            /*
             *     FU Indicator
             *    0 1 2 3 4 5 6 7
             *   +-+-+-+-+-+-+-+-+
             *   |F|NRI|  Type   |
             *   +---------------+
             */
    
            /*
             *      FU Header
             *    0 1 2 3 4 5 6 7
             *   +-+-+-+-+-+-+-+-+
             *   |S|E|R|  Type   |
             *   +---------------+
             */
    
            int pktNum = frameSize / RTP_MAX_PKT_SIZE;       // 有几个完整的包
            int remainPktSize = frameSize % RTP_MAX_PKT_SIZE; // 剩余不完整包的大小
            int i, pos = 1;
    
            /* 发送完整的包 */
            for (i = 0; i < pktNum; i++)
            {
        
                rtpPacket->payload[0] = (naluType & 0x60) | 28;
                rtpPacket->payload[1] = naluType & 0x1F;
                
                if (i == 0) //第一包数据
                    rtpPacket->payload[1] |= 0x80; // start
                else if (remainPktSize == 0 && i == pktNum - 1) //最后一包数据
                    rtpPacket->payload[1] |= 0x40; // end
    
                memcpy(rtpPacket->payload+2, frame+pos, RTP_MAX_PKT_SIZE);
                ret = rtpSendPacket(socket, ip, port, rtpPacket, RTP_MAX_PKT_SIZE+2);
                if(ret < 0)
                    return -1;
    
                rtpPacket->rtpHeader.seq++;
                sendBytes += ret;
                pos += RTP_MAX_PKT_SIZE;
            }
    
            /* 发送剩余的数据 */
            if (remainPktSize > 0)
            {
        
                rtpPacket->payload[0] = (naluType & 0x60) | 28;
                rtpPacket->payload[1] = naluType & 0x1F;
                rtpPacket->payload[1] |= 0x40; //end
    
                memcpy(rtpPacket->payload+2, frame+pos, remainPktSize+2);
                ret = rtpSendPacket(socket, ip, port, rtpPacket, remainPktSize+2);
                if(ret < 0)
                    return -1;
    
                rtpPacket->rtpHeader.seq++;
                sendBytes += ret;
            }
        }
    
    out:
    
        return sendBytes;
    }
    
    int main(int argc, char* argv[])
    {
        
        int socket;
        int fd;
        int fps = 25;
        int startCode;
        struct RtpPacket* rtpPacket;
        uint8_t* frame;
        uint32_t frameSize;
    
        fd = open(H264_FILE_NAME, O_RDONLY);
        if(fd < 0)
        {
        
            printf("failed to open %s\n", H264_FILE_NAME);
            return -1;
        }
    
        socket = createUdpSocket();
        if(socket < 0)
        {
        
            printf("failed to create socket\n");
            return -1;
        }
    
        rtpPacket = (struct RtpPacket*)malloc(500000);
        frame = (uint8_t*)malloc(500000);
    
        rtpHeaderInit(rtpPacket, 0, 0, 0, RTP_VESION, RTP_PAYLOAD_TYPE_H264, 0,
                        0, 0, 0x88923423);
    
        while(1)
        {
        
            frameSize = getFrameFromH264File(fd, frame, 500000);
            if(frameSize < 0)
            {
        
                printf("read err\n");
                continue;
            }
    
            if(startCode3(frame))
                startCode = 3;
            else
                startCode = 4;
    
            frameSize -= startCode;
            rtpSendH264Frame(socket, MULTICAST_IP, MULTICAST_PORT,
                                rtpPacket, frame+startCode, frameSize);
            rtpPacket->rtpHeader.timestamp += 90000/FPS;
    
            usleep(1000*1000/fps);
        }
    
        free(rtpPacket);
        free(frame);
    
        return 0;
    }

#### rtp.h ####

/*
     * 作者：_JT_
     * 博客：https://blog.csdn.net/weixin_42462202
     */
    
    #ifndef _RTP_H_
    #define _RTP_H_
    #include <stdint.h>
    
    #define RTP_VESION              2
    
    #define RTP_PAYLOAD_TYPE_H264   96
    #define RTP_PAYLOAD_TYPE_AAC    97
    
    #define RTP_HEADER_SIZE         12
    #define RTP_MAX_PKT_SIZE        1400
    
    /*
     *
     *    0                   1                   2                   3
     *    7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0
     *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     *   |V=2|P|X|  CC   |M|     PT      |       sequence number         |
     *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     *   |                           timestamp                           |
     *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     *   |           synchronization source (SSRC) identifier            |
     *   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
     *   |            contributing source (CSRC) identifiers             |
     *   :                             ....                              :
     *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     *
     */
    struct RtpHeader
    {
        
        /* byte 0 */
        uint8_t csrcLen:4;
        uint8_t extension:1;
        uint8_t padding:1;
        uint8_t version:2;
    
        /* byte 1 */
        uint8_t payloadType:7;
        uint8_t marker:1;
        
        /* bytes 2,3 */
        uint16_t seq;
        
        /* bytes 4-7 */
        uint32_t timestamp;
        
        /* bytes 8-11 */
        uint32_t ssrc;
    };
    
    struct RtpPacket
    {
        
        struct RtpHeader rtpHeader;
        uint8_t payload[0];
    };
    
    void rtpHeaderInit(struct RtpPacket* rtpPacket, uint8_t csrcLen, uint8_t extension,
                        uint8_t padding, uint8_t version, uint8_t payloadType, uint8_t marker,
                       uint16_t seq, uint32_t timestamp, uint32_t ssrc);
    int rtpSendPacket(int socket, const char* ip, int16_t port, struct RtpPacket* rtpPacket, uint32_t dataSize);
    
    #endif //_RTP_H_

#### rtp.c ####

/*
     * 作者：_JT_
     * 博客：https://blog.csdn.net/weixin_42462202
     */
    
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <arpa/inet.h>
    #include <netinet/in.h>
    #include <arpa/inet.h>
    
    #include "rtp.h"
    
    void rtpHeaderInit(struct RtpPacket* rtpPacket, uint8_t csrcLen, uint8_t extension,
                        uint8_t padding, uint8_t version, uint8_t payloadType, uint8_t marker,
                       uint16_t seq, uint32_t timestamp, uint32_t ssrc)
    {
        
        rtpPacket->rtpHeader.csrcLen = csrcLen;
        rtpPacket->rtpHeader.extension = extension;
        rtpPacket->rtpHeader.padding = padding;
        rtpPacket->rtpHeader.version = version;
        rtpPacket->rtpHeader.payloadType =  payloadType;
        rtpPacket->rtpHeader.marker = marker;
        rtpPacket->rtpHeader.seq = seq;
        rtpPacket->rtpHeader.timestamp = timestamp;
        rtpPacket->rtpHeader.ssrc = ssrc;
    }
    
    int rtpSendPacket(int socket, const char* ip, int16_t port, struct RtpPacket* rtpPacket, uint32_t dataSize)
    {
        
        struct sockaddr_in addr;
        int ret;
    
        addr.sin_family = AF_INET;
        addr.sin_port = htons(port);
        addr.sin_addr.s_addr = inet_addr(ip);
    
        rtpPacket->rtpHeader.seq = htons(rtpPacket->rtpHeader.seq);
        rtpPacket->rtpHeader.timestamp = htonl(rtpPacket->rtpHeader.timestamp);
        rtpPacket->rtpHeader.ssrc = htonl(rtpPacket->rtpHeader.ssrc);
    
        ret = sendto(socket, (void*)rtpPacket, dataSize+RTP_HEADER_SIZE, 0,
                        (struct sockaddr*)&addr, sizeof(addr));
    
        rtpPacket->rtpHeader.seq = ntohs(rtpPacket->rtpHeader.seq);
        rtpPacket->rtpHeader.timestamp = ntohl(rtpPacket->rtpHeader.timestamp);
        rtpPacket->rtpHeader.ssrc = ntohl(rtpPacket->rtpHeader.ssrc);
    
        return ret;
    }

## 四、测试 ##

将`multicast.c`、`rtp.h`、`rtp.c`保存下来

编译运行，程序默认会打开`test.h264`的视频文件，如果你没有视频源的话，可以从[RtspServer][]的example目录下获取

# gcc multicast.c rtp.c
    # ./a.out

将sdp保存为multicast.sdp

a=type:broadcast
    a=rtcp-unicast: reflection
    m=video 9832 RTP/AVP 96
    c=IN IP4 239.255.255.11/255
    a=rtpmap:96 H264/90000
    a=framerate:25

使用vlc打开sdp文件

# vlc multicast.sdp

*  运行效果
    
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MjQ2MjIwMg_size_16_color_FFFFFF_t_70 1]

[-RtspServer]: https://blog.csdn.net/weixin_42462202/article/details/98956346
[RTSP_RTSP]: https://blog.csdn.net/weixin_42462202/article/details/98986535
[RTSP_RTSP 1]: https://blog.csdn.net/weixin_42462202/article/details/99068041
[RTSP_RTP_H.264]: https://blog.csdn.net/weixin_42462202/article/details/99089020
[RTSP_H.264_RTSP]: https://blog.csdn.net/weixin_42462202/article/details/99111635
[RTSP_RTP_AAC]: https://blog.csdn.net/weixin_42462202/article/details/99200935
[RTSP_AAC_RTSP]: https://blog.csdn.net/weixin_42462202/article/details/99311193
[RTSP_RTP]: https://blog.csdn.net/weixin_42462202/article/details/99329048
[RTSP_RTSP 2]: https://blog.csdn.net/weixin_42462202/article/details/99413781
[RTSP_RTP OVER RTSP_TCP_RTSP]: https://blog.csdn.net/weixin_42462202/article/details/99442338
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[RtspServer]: https://github.com/ImSjt/RtspServer
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