example/demo.py: video writer could not be opened

The video example does not work. I get the following error:

File "visdom_demo.py", line 28, in <module> viz.video(tensor=video) File "/home/bk17/anaconda3/envs/pytorch/lib/python3.6/site-packages/visdom/__init__.py", line 420, in video assert writer.isOpened(), 'video writer could not be opened' AssertionError: video writer could not be opened

I’m using the video mentioned in the code comments as the input file. The installed opencv version is 3.2.0

[bishesh]

Sorry, missed this for a while and then later was waiting to test OpenCV set-up properly before posting. The problem is with the choice of codec in fourcc variable in the code you linked above. Would it be possible to support other codecs (like letting user choose it) ?

fourcc = cv2.VideoWriter_fourcc(
                    chr(ord('T')),
                    chr(ord('H')),
                    chr(ord('E')),
chr(ord('O'))

I tried a simple test code in my set-up and it works for certain codecs but not with the one used in visdom:

import cv2
import torch
import numpy
t = torch.zeros(10,100,100,3)
t1 = torch.ones(100,100,3)
for idx in range(t.size()[0]):
    if idx % 3 == 0:
        t[idx,:,:,:] = t1
fw, fh = t.size()[1], t.size()[2]
fourcc = cv2.VideoWriter_fourcc(*'MJPG') # works
#fourcc = cv2.VideoWriter_fourcc(*'XVID') # Does not work
# fourcc = visdom fourcc also does not work

out = cv2.VideoWriter('../results/output.avi',fourcc, 2.0, (fw, fh))
assert out.isOpened(), 'video writer could not be opened'

for idx in range(t.size()[0]):
    out.write(t[idx,:,:,:].numpy())
out.release() 

[JackUrb]

@GregorKoehler - We haven’t revisited this, though we’d be happy to accept a PR that adds an optional flag to the python version of the video function for other codecs.