streaming with tcp using opencv and socket - sockets

Question

i have done simple tcp client/server program got working well with strings and character data...i wanted to take each frames(from a webcam) and sent it to server.. here is the part of client program where error happened:
line:66 if(send(sock, frame, sizeof(frame), 0)< 0)
error:
client.cpp:66:39: error: cannot convert ‘cv::Mat’ to ‘const void*’ for argument ‘2’ to ‘ssize_t send(int, const void*, size_t, int)
i cant recognise this error....kindly help...the following complete client program:
#include<stdio.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<string.h>
#include<stdlib.h>
#include<netdb.h>
#include<unistd.h>
#include "opencv2/objdetect.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/imgproc.hpp"
#include <iostream>
using namespace std;
using namespace cv;
int main(int argc,char *argv[])
{
int sock;
struct sockaddr_in server;
struct hostent *hp;
char buff[1024];
VideoCapture capture;
Mat frame;
capture.open( 1 );
if ( ! capture.isOpened() ) { printf("--(!)Error opening video capture\n"); return -1; }
begin:
capture.read(frame);
if( frame.empty() )
{
printf(" --(!) No captured frame -- Break!");
goto end;
}
sock=socket(AF_INET,SOCK_STREAM,0);
if(sock<0)
{
perror("socket failed");
exit(1);
}
server.sin_family =AF_INET;
hp= gethostbyname(argv[1]);
if(hp == 0)
{
perror("get hostname failed");
close(sock);
exit(1);
}
memcpy(&server.sin_addr,hp->h_addr,hp->h_length);
server.sin_port = htons(5000);
if(connect(sock,(struct sockaddr *) &server, sizeof(server))<0)
{
perror("connect failed");
close(sock);
exit(1);
}
int c = waitKey(30);
if( (char)c == 27 ) { goto end; }
if(send(sock, frame, sizeof(frame), 0)< 0)
{
perror("send failed");
close(sock);
exit(1);
}
goto begin;
end:
printf("sent\n",);
close(sock);
return 0;
}

Answer 1

Because TCP provides a stream of bytes, before you can send something over a TCP socket, you must compose the exact bytes you want to send. Your use of sizeof is incorrect. The sizeof function tells you how many bytes are needed on your system to store the particular type. This bears no relationship to the number of bytes the data will require over the TCP connection which depends on the particular protocol layered on top of TCP you are implementing which must specify how data is to be sent at the byte level.

Answer 2

like david already said, you got the length wrong. sizeof() won't help, what you want is probably
frame.total() * frame.channels()
you can't send a Mat object, but you can send the pixels ( the data pointer ) , so this would be:
send(sock, frame.data,frame.total() * frame.channels(), 0)
but still a bad idea. sending uncompressed pixels over the netwotrk ? bahh.
please look at imencode/imdecode
i'm pretty sure, you got the client / server roles in reverse here.
usually the server holds the information to retrieve ( the webcam ), and the client connects to that
and requests an image.