请教一个UDP组播的问题

[daydreary]

用WinSend发送组播，发送的文件是一个TS流，从物理机windows往虚拟机Linux系统上发。接收端程序是我写的，每次发送都是发出85866KB，但是接收的文件就要比这个小几百K。这样播放时候丢帧就会卡顿几下。附上代码，请高手指点下，谢谢。

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

#define MAX_LENGTH 5 * 1024 * 1024
#define PORT 8000
#define GROUP "239.1.1.1"

int main()
{
    struct sockaddr_in server, client;
    struct ip_mreq mreq;
    unsigned char buf[MAX_LENGTH];
    int fd, sinSize, recvlength;
    fd_set readfds;
    int ret;
    struct timeval timeout = {3, 0};
    
    memset(&server, 0, sizeof(struct sockaddr_in));
    memset(&client, 0, sizeof(struct sockaddr_in));
    memset(&mreq, 0, sizeof(struct ip_mreq));
    
    server.sin_family = AF_INET;
    server.sin_port = htons(PORT);
    if (inet_aton(GROUP, &server.sin_addr) < 0) {
        perror("inet_aton");
        return -1;   
    }            
    
    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        perror("socket");
        return -1;    
    }
    
    if (bind(fd, (struct sockaddr *) &server, sizeof(server)) < 0) {
        perror("bind");
        return -1;
    }
    
    if (inet_aton(GROUP, &mreq.imr_multiaddr) < 0) {
        perror("inet_aton mreq.imr_multiaddr");
        return -1;   
    }  
    inet_aton("192.168.180.170", &(mreq.imr_interface));
    if (setsockopt(fd, SOL_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)) < 0) {
        perror("setsockopt");
        return -1;
    }
    
    sinSize = sizeof(client);
    FILE *fp;
    fp = fopen("./recv1.2.ts", "ab+");
    while (1) {
        FD_ZERO(&readfds);
        FD_SET(fd, &readfds);
        if ((ret = select(fd + 1, &readfds, NULL, NULL, &timeout)) < 0) 
            break;
        else if(ret == 0)
            continue;
        else {
            if (FD_ISSET(fd, &readfds) == 0) 
                continue;
            recvlength = recvfrom(fd, buf, MAX_LENGTH, 0, (struct sockaddr *) &client, &sinSize);
            if (recvlength < 0) {
                perror("receive");
                continue;    
            }
            fwrite(buf, sizeof(unsigned char), recvlength, fp);
            fflush(fp);
        }
    }
}