VIDEOIO ERROR from opencv ONLY when streaming with flask - opencv

Question

I know that this is an opencv error, and I know that Flask has nothing to do with opencv. However, please stick with me through the end.
I'm getting this really weird error ONLY when I'm streaming the CV frames:
VIDEOIO ERROR: V4L2: Pixel format of incoming image is unsupported by OpenCV
Unable to stop the stream: Device or resource busy
My code:
// my camera_detector class does some AI works on the camera frame, other than that nothing special
camera = camera_detector(my_arguments)
#app.route('/')
def index():
return render_template('index.html')
def gen(camera):
while True:
print('getting frame')
frame = camera.get_frame()
yield (b'--frame\r\n'
b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n\r\n')
#app.route('/feed')
def video_feed():
return Response(gen(camera), mimetype='multipart/x-mixed-replace; boundary=frame')
Now here is why I said this only happens with Flask, if I just grab the camera frame like this:
while True:
frame = camera.get_frame()
without ever using flask, everything runs just fine o_0
If it makes any difference, I'm using python3.7 on the pi4. My camera also does some AI works on camera_frame produced by open cv, draw boxes, labels, before returning the frame to Flask:
def get_frame(self):
ret, frame = self.camera.read()
# processing, does AI works, draw boxes and labels
ret, jpeg = cv2.imencode('.jpg', frame)
return jpeg.tobytes()
[Edit] camera info if it helps:
{20-04-22 15:39}raspberrypi:~/detect pi% v4l2-ctl -d /dev/video0 --list-formats
ioctl: VIDIOC_ENUM_FMT
Type: Video Capture
[0]: 'YUYV' (YUYV 4:2:2)
[1]: 'MJPG' (Motion-JPEG, compressed)
[SOLVED]: Answer is below for those who are interested.

Answer 1

For those who got had the same issue, I found out what was causing it. The problem was that I created a camera instance like this:
camera = camera_detector(my_arguments)
and then passed that into my route function:
#app.route('/feed')
def video_feed():
return Response(gen(camera), mimetype='multipart/x-mixed-replace; boundary=frame')
Turn out opencv did not like that so much. I found this very odd, but it works fine after I changed it to:
#app.route('/feed')
def video_feed():
return Response(gen(camera_detector(my_arguments)), mimetype='multipart/x-mixed-replace; boundary=frame')
Any body who have an explanation for this would be nice!

Answer 2

It looks like you're borrowing code from https://blog.miguelgrinberg.com/post/video-streaming-with-flask
Comparing the two, your snippet has an extra \r\n' at the end of each frame. Try removing that.