A basic method to measure video fps using OpenCV's countNonZero function.

framerateMeasure.py

def framerateMeasure(pngPath, csvPath, rate):
    start = time()
    differenceValues = []
    for i in range(rate):
        differenceValues.append(0)
    
    fields=['Frame','FPS']
    writeCSV(fields, csvPath)

    j = 1
    # len(os.listdir(pngPath))-1
    for x in range(len(os.listdir(pngPath))-1):
        img1 = cv.imread(pngPath + str(j) + ".png")
        j = j + 1
        img2 = cv.imread(pngPath + str(j) + ".png")
        difference = cv.subtract(img1, img2)
        diffImg = cv.cvtColor(difference, cv.COLOR_BGR2GRAY)
        nzCount = cv.countNonZero(diffImg)

        if nzCount == 0:
            # Dupe Frame
            differenceValues.pop(0)
            differenceValues.append(0)
        else:
            # New frame
            differenceValues.pop(0)
            differenceValues.append(1)

        
        updateCSV(calcFPS(differenceValues), x, csvPath)