why the frame is not equal with opencv?

why the frame is not equal with opencv? my test code as below,please give me an answer,thank you!
```
from decord import VideoReader,cpu,gpu,VideoLoader
import cv2
import numpy as np
def frame_reader(video_path):
video_capture = cv2.VideoCapture()
if not video_capture.open(video_path):
video_capture.release()
return
ret = 1
cnt = 0
res = []
while ret:
if cnt >=5:
break
ret,frame = video_capture.read()
res.append(frame)
cnt +=1
video_capture.release()
return res
res = frame_reader('/data/zhoup/workspace/videoDecode/examples/preview.mp4')
vr = VideoReader('/data/zhoup/workspace/videoDecode/examples/preview.mp4', ctx=cpu(0))
lists = [0,1,2,3,4]
frames = vr.get_batch(lists).asnumpy()
for i in range(len(lists)):
v1 = res[i]
v2 = frames[i]
equal = (v1==v2).all()
print(equal)

```