How to stream a opencv Mat with ffmpeg in c++

Question

I'm new here. I'm trying to stream some images processed with opencv on a LAN using ffmpeg. I saw this: Pipe raw OpenCV images to FFmpeg but it doesn't work for me, it creates only noise. I think the data I'm sending are not in the right format. I also have a look to this: How to send opencv video's to ffmpeg but (looking at the last answer) the option -f jpeg_pipe give me error.

What I do now:

I have a RGB Mat called "composedImage"
I send in output with: std::cout << composedImage; The output are the pixels values separated by comma
then I call:

./example | ffmpeg -f rawvideo -pixel_format bgr24 -video_size 160x120 -framerate 20 -i - -f udp://192.168.1.79:1234

I try to read using VLC (it didn't work) and with ffplay:

ffplay -f rawvideo -pixel_format gray -video_size 160x120 -framerate 30 udp://192.168.1.79:1234

Here it seems so easy: http://ffmpeg.org/ffmpeg-formats.html#rawvideo

I have also tried to write the image and sent it, but I have errors. Probably it tries to send before the image is complete.

Thank you for your help.

You said you got an error, but what's the error? Also, my gut says you'll have to put std::cout in binary mode for this to work. — Stephen Newell, Feb 27 '18 at 16:55
do you have an example where anyone uses cout to stream frames? — Micka, Feb 27 '18 at 19:36
@micka: no I don't have examples. I'm not even sure on how a stream should be (what ffmepg expects) — cristian b, Mar 02 '18 at 11:20

score 3 · Accepted Answer · answered Feb 27 '18 at 23:19

I managed to stream, albeit with potato quality, maybe some ffmpeg guru can help out with the ffmpeg commands.

#include <iostream>                                                          
#include <opencv2/opencv.hpp>                                                
#include <vector>                                      

using namespace cv;                                                          

int main() {                                                                 
    VideoCapture cap("Your video or stream goes here");
    Mat frame;                                                               
    std::ios::sync_with_stdio(false);                                        

    while (cap.read(frame)) {                                                
        for (size_t i = 0; i < frame.dataend - frame.datastart; i++) 
           std::cout << frame.data[i];                                   
    }                                                                        

    return 0;                                                                
}

And then pipe it to ffmpeg like

./test | ffmpeg -f rawvideo -pixel_format bgr24 -video_size 1912x796 -re -framerate 20  -i - -f mpegts -preset ultrafast udp://127.0.0.1:1234

And play it with ffplay mpv or whatever

ffplay udp://127.0.0.1:1234

Thank you for the answer, this almost goes even if with some changes. I hope I can let it go properly — cristian b, Mar 02 '18 at 11:30
So, the printed values in output are ok, but when sending the streaming I have problems, it seems that the first block of the image is shown at the end of the frame instead of the beginning. At this point I think there are problems in the streaming. — cristian b, Mar 02 '18 at 16:26
yes, I've changed the resolution to mine, but the problem is not that. It seems the data are not well encoded, or at least their order. Thanks. — cristian b, Mar 02 '18 at 20:47
So, finally, I find that adding an offset in the for cycle (the number is found empirically) it works. Not very elegant, but for now is ok. — cristian b, Mar 05 '18 at 09:47

How to stream a opencv Mat with ffmpeg in c++

1 Answers1