decompressing video on different platforms, value of pixels differ

Question

I got the wrong pixel values between Swift iOS and OpenCV Python.

In Python, I read video with video.read() and got BGR 79, 82, 90 of the first pixel.

In Swift, I read the video by AVURLAsset and I got BGR 80, 84, 92.

It seems quite the same, but maybe there's some rounding here, isn't there? How can I deal with it? I really appreciate your help.

Here is some code to reproduce:

Python:

import cv2
vidcap = cv2.VideoCapture('test_video.mp4')
success, image = vidcap.read()

image[0][0] # output is [79, 82, 90]

Swift:

DispatchQueue.global().async(execute: {
        while reader?.status == AVAssetReader.Status.reading {
            if(rout.copyNextSampleBuffer() != nil){
                // Buffer of the frame to perform processing on
                let sampleBuffer: CMSampleBuffer = rout.copyNextSampleBuffer()!
                let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)
            }
            usleep(10000)
        }
    })

Extract pixel from first pixelBuffer and I got BGR [80, 84, 92]