Stream to Facebook Live using OpenCV

Question

I am planning to stream a video file to Facebook Live but I want to programmatically edit its frames like adding texts depending. My problem is that I don't know how to properly send data to Facebook Live. I tried ffmpeg but it doesn't work.

Here is my code that I tried

import subprocess
import cv2

rtmp_url = "rtmps://live-api-s.facebook.com:443/rtmp/FB-1081417119476224-0-AbwwMK91tFTjFy2j"

path = "7.mp4"
cap = cv2.VideoCapture(path)

# gather video info to ffmpeg
fps = int(cap.get(cv2.CAP_PROP_FPS))
width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))

# command and params for ffmpeg
command = ['ffmpeg',
           '-y',
           '-f', 'rawvideo',
           '-vcodec', 'rawvideo',
           '-pix_fmt', 'bgr24',
           '-s', f"{width}x{height}",
           '-r', str(fps),
           '-i', '-',
           '-c:v', 'libx264',
           '-pix_fmt', 'yuv420p',
           '-preset', 'ultrafast',
           '-f', 'flv',
           rtmp_url]

# using subprocess and pipe to fetch frame data
p = subprocess.Popen(command, stdin=subprocess.PIPE)

while cap.isOpened():
    ret, frame = cap.read()
    if not ret:
        print("frame read failed")
        break

    # YOUR CODE FOR PROCESSING FRAME HERE

    # write to pipe
    p.stdin.write(frame.tobytes())