How to Detect Speaker from facial landmarks of mouth using face_recognition

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I am trying to find a speaker from a webcam using facial land marks which i can get using the face_recognition library. I am successful in getting the month top lip and bottom lip points.

I want to calculate the distance b/w these points and according to distance may be we can say person is speaking or not. What i had done so far now.

import face_recognition
import cv2
import math


video_capture = cv2.VideoCapture(0)
while True:
    # Grab a single frame of video
    ret, frame = video_capture.read()

    face_landmarks = face_recognition.face_landmarks(frame)
    try:
        p1=face_landmarks[0]['top_lip']
        p2=face_landmarks[0]['bottom_lip']
        x1,y1=p1[9]
        x3,y3=p1[8]
        x4,y4=p1[10]
        x2,y2=p2[9]
        x5,y5=p2[8]
        x6,y6=p2[10]
        dist = math.sqrt(((x2+x5+x6) - (x1+x3+x4)) ** 2 + ((y2+y5+y6) - (y1+y3+y4)) ** 2)
        print(dist)
        image = cv2.circle(frame, p1[8], 1, (255, 255, 255, 0), 2)
        image = cv2.circle(frame, p1[9], 1, (255, 255, 255, 0), 2)
        image = cv2.circle(frame, p1[10], 1, (255, 255, 255, 0), 2)

        image = cv2.circle(frame, p2[8], 1, (255, 255, 255, 0), 2)
        image = cv2.circle(frame, p2[9], 1, (255, 255, 255, 0), 2)
        image = cv2.circle(frame, p2[10], 1, (255, 255, 255, 0), 2)
        # # cv2.clipLine(frame, p1, p2,(255,255,255,0), thickness=2)
        # for p1t in p1:
        #     image = cv2.circle(frame, p1t, 1, (255,255,255,0), 2)
        # for p1b in p2:
        #     image = cv2.circle(frame, p1b, 1, (255, 255, 255, 0), 2)

        cv2.namedWindow('Video', cv2.WINDOW_NORMAL)
        cv2.imshow('Video', frame)
    except Exception as e:
        raise(e)

    # Hit 'q' on the keyboard to quit!
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break



video_capture.release()
cv2.destroyAllWindows()

but the distance which i had calculated is varying even if person don't speak.If anyone has idea that how i can detect speaker using month lands marks then please let me know. Thanks