Code in python to extract Heart Rate from video from green channel frame

Question

this is my code but the heart rate value is not accurate. Please help me how to improve it. normal bpm should be 60-100. I am trying to extract the hr by taking the green channel, then calc the fft frequency of it, then find the peaks and filter them, and then count the peaks, and then convert it to bpm. Ofcourse this way based on some articles and now I want to implement it.

import numpy as np
from scipy.signal import find_peaks

class ExtractHeartRate:
   def __init__(self, green_channel, timer):
    self.green_channel = green_channel  # Green channel of the frame
    self.timer = timer
    self.heart_rate = 0

   def calc_hr_process(self):
    # Perform FFT on the Green Channel
    fft_result = np.fft.fft(self.green_channel)
    fft_result = np.abs(fft_result).flatten()
    fft_freq = np.fft.fftfreq(len(fft_result))

    # Locate peaks in the necessary frequency range
    peaks, _ = find_peaks(fft_result, height=0, threshold=0)

    # Filter peaks within the necessary frequency range
    valid_peaks = peaks[(fft_freq[peaks] >= 0.48) & (fft_freq[peaks] <= 4)]

    # Count the peaks within a set time range
    elapsed_time = self.timer.elapsed() / 1000  # Elapsed time in seconds
    if elapsed_time > 0:
        # Calculate the peak count within the set time range
        peak_count = len(valid_peaks)

        # Calculate the heart rate
        heart_rate = peak_count * 60 / elapsed_time  # Convert to BPM using elapsed time
        self.heart_rate = round(heart_rate)
    else:
        self.heart_rate = 0
    return self.heart_rate