[FIXED] qt.qpa.xcb: could not connect to display when using yolov4-custom-functions


I am using https://github.com/theAIGuysCode/yolov4-custom-functions this repository. I want to crop and save pictures while running on webcam. But when I run the following code:

python detect_video.py --weights ./checkpoints/yolov4-416 --size 416 --model yolov4 --video ./data/video/bobinmi.mp4 --output ./detections/results.avi --crop

I can just detect the first frame of the video. Then it gives error and not detect. What should I do?

I’m using CUDA 10.1, Python 3.7 and Tensorflow 2.3. The error is same in CPU and GPU working environments.

The error message is:

FPS: 1.50
qt.qpa.xcb: could not connect to display 
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "/usr/local/lib/python3.7/dist-packages/cv2/qt/plugins" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: xcb.

Fatal Python error: Aborted

Current thread 0x00007fbeed09b780 (most recent call first):
  File "detect_video.py", line 165 in main
  File "/usr/local/lib/python3.7/dist-packages/absl/app.py", line 254 in _run_main
  File "/usr/local/lib/python3.7/dist-packages/absl/app.py", line 308 in run
  File "detect_video.py", line 178 in <module>

Second problem is when I use this command:

!python detect_video.py --weights ./checkpoints/yolov4-416 --size 416 --model yolov4 --video 0 --output ./detections/results2.avi --crop

then it says:

[ WARN:0@5.489] global /io/opencv/modules/videoio/src/cap_v4l.cpp (902) open VIDEOIO(V4L2:/dev/video0): can't open camera by index
Video has ended or failed, try a different video format!

I know the problem is with opening the camera in Colab. But I couldn’t find how to solve it.


The error message is only caused in Colab at line 165, that is with the following instruction:

cv2.namedWindow("result", cv2.WINDOW_AUTOSIZE)

From the documentation this function is used to create a window.
The reason is that Colab does not have a screen and some cv2 functions need a screen to perform the operations. Creating a windows is definitely one of them.

To fix the error in Colab should be enough to install a virtual screen. The code (from this stack answer):

!apt-get install -y xvfb # Install X Virtual Frame Buffer
import os
os.system('Xvfb :1 -screen 0 1600x1200x16  &')    # create virtual display with size 1600x1200 and 16 bit color. Color can be changed to 24 or 8
os.environ['DISPLAY']=':1.0'    # tell X clients to use our virtual DISPLAY :1.0

Answered By – ClaudiaR

Answer Checked By – Senaida (Easybugfix Volunteer)

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