c语言编写rtp接收代码并组成h264帧

要编写一个基于C语言的RTP接收代码并组成H.264帧，可以按照以下步骤进行：

1. 创建一个UDP套接字并绑定到一个端口上，以接收RTP包。

int socket_fd = socket(AF_INET, SOCK_DGRAM, 0);  // 创建UDP套接字
struct sockaddr_in local_addr;
memset(&local_addr, 0, sizeof(local_addr));
local_addr.sin_family = AF_INET;
local_addr.sin_addr.s_addr = htonl(INADDR_ANY);  // 接收所有IP地址发送的数据
local_addr.sin_port = htons(rtp_port);  // 绑定到RTP端口号
bind(socket_fd, (struct sockaddr*)&local_addr, sizeof(local_addr));

2. 接收RTP包并解析其中的头部信息，包括序列号、时间戳等。

char rtp_packet[1500];
struct sockaddr_in remote_addr;
unsigned int addr_len = sizeof(remote_addr);
recvfrom(socket_fd, rtp_packet, sizeof(rtp_packet), 0, (struct sockaddr*)&remote_addr, &addr_len);

// 解析RTP头部信息
unsigned char payload_type = rtp_packet[1] & 0x7f;  // RTP负载类型
unsigned short sequence_number = ntohs(*(unsigned short*)(rtp_packet + 2));  // RTP序列号
unsigned int timestamp = ntohl(*(unsigned int*)(rtp_packet + 4));  // RTP时间戳
unsigned int ssrc = ntohl(*(unsigned int*)(rtp_packet + 8));  // RTP同步信源标识符

3. 解析RTP负载数据，将之前分割的NALU序列组合成一帧H.264码流。

unsigned char* payload_data = rtp_packet + 12;  // RTP负载数据
unsigned int payload_len = ntohs(*(unsigned short*)(rtp_packet + 2)) - 12;  // RTP负载长度

while (payload_len > 0) {
    // 解析NALU头部信息
    unsigned char nal_unit_type = payload_data[0] & 0x1f;
    unsigned char nal_ref_idc = (payload_data[0] >> 5) & 0x03;

    // 将NALU序列组合成一帧H.264码流
    if (nal_unit_type == 7 || nal_unit_type == 8) {
        // SPS或PPS单独组成一帧
        if (frame_pos > 0) {
            // 发送前面组合的帧
            send_h264_frame(h264_frame, frame_pos);
            frame_pos = 0;
        }
        memcpy(h264_frame, start_code, 4);
        memcpy(h264_frame + 4, payload_data, payload_len);
        frame_pos = 4 + payload_len;
    } else {
        // 其他类型NALU组成一帧
        if (frame_pos + 4 + payload_len > MAX_FRAME_SIZE) {
            // 超过最大帧长度，发送当前组合的帧
            send_h264_frame(h264_frame, frame_pos);
            frame_pos = 0;
        }
        memcpy(h264_frame + frame_pos, start_code, 4);
        memcpy(h264_frame + frame_pos + 4, payload_data, payload_len);
        frame_pos += 4 + payload_len;
    }

    // 跳过当前NALU
    payload_data += payload_len;
    payload_len = ntohs(*(unsigned short*)payload_data);
    payload_data += 2;
}

4. 发送组合好的H.264帧。

void send_h264_frame(unsigned char* frame_data, unsigned int frame_len) {
    // 发送一帧H.264码流
    sendto(socket_fd, frame_data, frame_len, 0, (struct sockaddr*)&remote_addr, sizeof(remote_addr));
}