OSError: Video 0 cannot be opened

[sohail759]

nvidia@nvidia-desktop:~/Desktop/py$ python3 demo.py --model human-pose-estimation-3d.pth --video 0
Traceback (most recent call last):
File "demo.py", line 86, in
for frame in frame_provider:
File "/home/nvidia/Desktop/CONVSYS/daniil/py/modules/input_reader.py", line 36, in iter
raise IOError('Video {} cannot be opened'.format(self.file_name))
OSError: Video 0 cannot be opened
##################################################
i am trying this code on my jetson nano.
opencv ==>4.1.0
webcam=>logitech 270
please help me to resolve this problem.