对g.711aRTP封装并发送C语言

以下是一个简单的示例代码，用于封装并发送G.711a RTP数据包，需要使用socket编程库：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define RTP_VERSION 2
#define RTP_PAYLOAD_TYPE 8
#define RTP_MARKER_BIT 0
#define RTP_SSRC 0x12345678
#define RTP_TIMESTAMP_INC 160

struct rtp_header {
    unsigned char csrc_count:4;
    unsigned char extension_bit:1;
    unsigned char padding_bit:1;
    unsigned char version:2;
    unsigned char payload_type:7;
    unsigned char marker_bit:1;
    unsigned short sequence_number;
    unsigned int timestamp;
    unsigned int ssrc;
    unsigned int csrc[1];
};

int main(int argc, char **argv)
{
    if (argc != 4) {
        fprintf(stderr, "Usage: %s <ipaddr> <port> <g711a_file>\n", argv[0]);
        exit(1);
    }

    char *ipaddr = argv[1];
    int port = atoi(argv[2]);
    char *g711a_file = argv[3];

    // 打开G.711a文件
    FILE *fp = fopen(g711a_file, "rb");
    if (fp == NULL) {
        perror("fopen");
        exit(1);
    }

    // 创建UDP socket
    int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }

    // 设置socket参数
    int optval = 1;
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) < 0) {
        perror("setsockopt");
        exit(1);
    }

    // 构造目标地址结构体
    struct sockaddr_in addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = inet_addr(ipaddr);
    addr.sin_port = htons(port);

    // 构造RTP数据包头部
    struct rtp_header *header = malloc(sizeof(struct rtp_header));
    memset(header, 0, sizeof(struct rtp_header));
    header->version = RTP_VERSION;
    header->padding_bit = 0;
    header->extension_bit = 0;
    header->csrc_count = 0;
    header->marker_bit = RTP_MARKER_BIT;
    header->payload_type = RTP_PAYLOAD_TYPE;
    header->ssrc = htonl(RTP_SSRC);
    header->timestamp = htonl(0);

    // 发送G.711a RTP数据包
    unsigned short seq_num = 0;
    unsigned int timestamp = 0;
    unsigned char buf[160];
    while (1) {
        int ret = fread(buf, 1, sizeof(buf), fp);
        if (ret <= 0) {
            break;
        }

        // 更新RTP数据包头部中的序列号和时间戳
        header->sequence_number = htons(seq_num++);
        header->timestamp = htonl(timestamp);
        timestamp += RTP_TIMESTAMP_INC;

        // 发送RTP数据包
        sendto(sockfd, header, sizeof(struct rtp_header), 0, (struct sockaddr *)&addr, sizeof(addr));
        sendto(sockfd, buf, ret, 0, (struct sockaddr *)&addr, sizeof(addr));
    }

    // 关闭文件和socket
    fclose(fp);
    close(sockfd);

    return 0;
}

这个示例代码中，我们打开一个G.711a文件，读取其中的音频数据，将其封装成RTP数据包并发送到指定的IP地址和端口。在RTP数据包中，我们使用了G.711a对应的payload type为8，同时使用了0x12345678作为SSRC。封装RTP数据包时，我们通过循环不断更新RTP数据包头部中的序列号和时间戳。