Frames getting distorted after passing through v4l2loopback

[nishanth-hon]

Step 2: Describe your environment

• v4l2loopback version: 0.12.3

• kernel version: Linux buildroot 4.19.81-g7fe3e10f1fdf-dirty #2 SMP PREEMPT Mon Dec 20 12:19:27 IST 2021 aarch64 GNU/Linux

• Distribution (+version): (not a standard distribution, custom buildroot os)

Step 3: Describe the problem:

I am planning to use camera from two different processes. when trying to read frames / write video through opencv-python, after passing through v4l2loopback, frames are getting distorted

Steps to reproduce:

1. modprobe v4l2loopback
2. gst-launch1.0 v4l2src device=/dev/video0 ! v4l2sink device=/dev/video1
3. write video using opencv-python 3.4.9 ( pasted code below)

Observed Results:

sample 1:

sample 2:

sample 3: (not all frames look distorted)

Expected Results:

Normal frames without distortion

Relevant Code:

code I am using to write video

import cv2
import time

cap = cv2.VideoCapture(1)
fourcc = cv2.VideoWriter_fourcc(*'mp4v')
out = cv2.VideoWriter('output.mp4', fourcc, 24, (1920, 1080))
print(cap.isOpened())

start = time.time()
while (time.time() - start) < 10:
    ret, frame = cap.read()
    if not ret:
        break

    out.write(frame)

out.release()
cap.release()

I understand if this is not reproducible, because I am not using a standard x86_64 distro. If that is the case, Any suggestions on how to work around this problem would be very useful.

Thanks in advance.

[umlaeute]

I am planning to use camera from two different processes.

does that mean you try to attach to consumers (aka: capture processes) to a single /dev/video (loopback) device? this is not supported (see https://github.com/umlaeute/v4l2loopback/pull/447#issuecomment-1002160400)