how to solve problem of low fps in OpenCV

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I took this sample code, but i have low fps during code execution

#include "opencv2/objdetect/objdetect.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"

#include <iostream>

using namespace std;
using namespace cv;

/** Função principal */
void detectAndDisplay(Mat frame);

/** Global rariaveis */
String face_cascade_name = "C:\\opencv\\sources\\data\\haarcascades\\haarcascade_frontalface_alt.xml";
String eyes_cascade_name = "C:\\opencv\\sources\\data\\haarcascades\\haarcascade_eye.xml";
String nose_cascade_name = "C:\\opencv\\sources\\data\\haarcascades\\haarcascade_mcs_nose.xml";
CascadeClassifier face_cascade;
CascadeClassifier eyes_cascade;
CascadeClassifier nose_cascade;
string window_name = "Capturando - Rosto detectado";
RNG rng(12345);

/** @funcão main */
int main(int argc, const char** argv)
{
    VideoCapture vcap(0);
    if (!vcap.isOpened()) {
        cout << "Erro ao abrir o video" << endl;
        return -1;
    }
    Mat frame;

    //-- 1. Carrega as biblioteca Cascade, responsavel por mapear o rosto.
    if (!face_cascade.load(face_cascade_name)) { printf("--(!)Erro ao carregar\n"); return -1; };
    if (!eyes_cascade.load(eyes_cascade_name)) { printf("--(!)Erro ao carregar\n"); return -1; };
    if (!nose_cascade.load(nose_cascade_name)) { printf("--(!)Erro ao carregar\n"); return -1; };

    //-- 2. Ler o video

    while (true)
    {
        vcap >> frame;
        //-- 3.Aplicação para captura os frames
        if (!frame.empty())
        {
            detectAndDisplay(frame);
        }
        else
        {
            printf(" --(!) No captured frame -- Break!"); break;
        }

        int c = waitKey(1);
        if ((char)c == 'c') { break; }
    }
    return 0;
}

/** @Função para detectar e mostrar */
void detectAndDisplay(Mat frame)
{
    std::vector<Rect> faces;
    Mat frame_gray;

    cvtColor(frame, frame_gray, COLOR_BGR2GRAY);
    equalizeHist(frame_gray, frame_gray);

    //-- Detecta rosto
    face_cascade.detectMultiScale(frame_gray, faces, 1.1, 2, 0 | CASCADE_SCALE_IMAGE, Size(30, 30));
    for (size_t i = 0; i < faces.size(); i++)
    {
        Point center(faces[i].x + faces[i].width*0.5, faces[i].y + faces[i].height*0.5);
        rectangle(frame, Point(faces[i].x, faces[i].y), Point(faces[i].x + faces[i].width, faces[i].y + faces[i].height), Scalar(255, 0, 0), 3, 8);
        Mat faceROI = frame_gray(faces[i]);
        vector<Rect> eyes;
        vector<Rect> noses;
        //-- detectar nariz e olhos
        eyes_cascade.detectMultiScale(faceROI, eyes, 1.1, 2, 0 | CASCADE_SCALE_IMAGE, Size(30, 30));
        for (size_t j = 0; j < eyes.size(); j++)
        {
            Point center(faces[i].x + eyes[j].x + eyes[j].width*0.5, faces[i].y + eyes[j].y + eyes[j].height*0.5);
            int radius = cvRound((eyes[j].width + eyes[j].height)*0.25);
            circle(frame, center, radius, Scalar(255, 0, 0), 4, 8, 0);
        }
        nose_cascade.detectMultiScale(faceROI, noses, 1.1, 2, 0 | CASCADE_SCALE_IMAGE, Size(30, 30));
        for (size_t j = 0; j < noses.size(); j++) {
            Point center(faces[i].x + noses[j].x + noses[j].width*0.5, faces[i].y + noses[j].y + noses[j].height*0.5);
            int radius = cvRound((noses[j].width + noses[j].height)*0.25);
            circle(frame, center, radius, Scalar(0, 0, 255), 4, 8, 0);
        }
    }
    //-- Show what you got
    imshow(window_name, frame);
}

while running, I get these errors or warnings

[ INFO:0] global C:\build\master_winpack-build-win64-vc15\opencv\modules\videoio\src\videoio_registry.cpp (187) cv::`anonymous-namespace'::VideoBackendRegistry::VideoBackendRegistry VIDEOIO: Enabled backends(7, sorted by priority): FFMPEG(1000); GSTREAMER(990); INTEL_MFX(980); MSMF(970); DSHOW(960); CV_IMAGES(950); CV_MJPEG(940)
[ INFO:0] global C:\build\master_winpack-build-win64-vc15\opencv\modules\videoio\src\backend_plugin.cpp (340) cv::impl::getPluginCandidates ...