Problems showing an image, ASSERT: "false" in file qasciikey.cpp

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Hello, I have a problem each time when I want to show a window on my screen. The next problem always appears: ASSERT: "false" in file qasciikey.cpp, line 501 The program has unexpectedly finished.

For example with the following code, the window is opened for a second and then the previous message appears and the program crashes.

int main(int, char**){

VideoCapture cap;

cap.open(string("/home/atierz/Documentos/Univrersidad/Vision/datos_practicas_1234_vison_computador/secuencias/sec_test.mp4"));
Mat frame;
namedWindow("video", 1);
for(;;){

    cap >>frame;
    if(!frame.data) break;
    imshow("video", frame);

    if (waitKey(5) >= 0)
        break;
}

}

Thanks in advance.