设置RTSP, RTP和RTCP端口号

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1.设置RTSP端口号

设置RTSP端口号的处理位于ARTSPConnection.cpp文件中，首先从url中获取端口号，如果读取不到，则设置为默认端口554。代码处理如下：

ARTSPConnection::ParseURL(    const char *colonPos = strchr(host->c_str(), ':');    if (colonPos != NULL) {        unsigned long x;        if (!ParseSingleUnsignedLong(colonPos + 1, &x) || x >= 65536) { // rtsp端口必须小于65536            return false;        }        *port = x;        size_t colonOffset = colonPos - host->c_str();        size_t trailing = host->size() - colonOffset;        host->erase(colonOffset, trailing);    } else {        *port = 554; // 如果从url中获取不到端口，则设置默认端口554    }

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2.设置RTP和RTCP端口号

设置RTP和RTCP端口号的处理位于ARTPConnection.cpp文件中中，与设置RTSP端口号的处理分别在不同的文件中。

（1）函数声明：创建一对相邻端口的UDP数据报套接字。rtp套接字是偶数端口，rtcp套接字端口比rtp端口号大一个号。

    // Creates a pair of UDP datagram sockets bound to adjacent ports    // (the rtpSocket is bound to an even port, the rtcpSocket to the    // next higher port).    static void MakePortPair(            int *rtpSocket, int *rtcpSocket, unsigned *rtpPort);

（2）函数定义：具体设置RTP和RTCP端口

// staticvoid ARTPConnection::MakePortPair(        int *rtpSocket, int *rtcpSocket, unsigned *rtpPort) {    *rtpSocket = socket(AF_INET, SOCK_DGRAM, 0);    CHECK_GE(*rtpSocket, 0);    bumpSocketBufferSize(*rtpSocket);    *rtcpSocket = socket(AF_INET, SOCK_DGRAM, 0);    CHECK_GE(*rtcpSocket, 0);    bumpSocketBufferSize(*rtcpSocket);    unsigned start = (rand() * 1000)/ RAND_MAX + 15550; // 最小端口号为15550    start &= ~1; // 与1取反后的值做与操作，结果就是start变成偶数，端口从偶数开始    for (unsigned port = start; port < 65536; port += 2) { // rtp最大端口号为65535，此时rtcp端口号为65536        struct sockaddr_in addr;        memset(addr.sin_zero, 0, sizeof(addr.sin_zero));        addr.sin_family = AF_INET;        addr.sin_addr.s_addr = htonl(INADDR_ANY);        addr.sin_port = htons(port);        if (bind(*rtpSocket,                 (const struct sockaddr *)&addr, sizeof(addr)) < 0) {            continue;        }        addr.sin_port = htons(port + 1);        if (bind(*rtcpSocket,                 (const struct sockaddr *)&addr, sizeof(addr)) == 0) {            *rtpPort = port;            return; // 绑定rtcp端口后返回        }    }    TRESPASS();}