cv2.VideoCapture(0, cv2.DSHOW) returns none-CodePudding

I'm trying to capture video from an in-build webcam on a laptop (or external USB camera) using opencv, specifically VideoCapture with the DSHOW argument. I know there is a way to set the resolution and even FPS, however the DirectShow argument for the API returns none when I included it in the code.

For example;

# returns my webcam's stream, but all optional arguments are ignored
camera = cv2.VideoCapture(0)
camera = cv2.VideoCapture(0, cv2.CAP_V4L2)

# returns none and loops infinitely or errors out when *if im.any()*
camera = cv2.VideoCapture(0, cv2.CAP_DSHOW)

This is the code that follows after the above;

# should set resolution, settings are always ignored
camera.set(cv2.CAP_PROP_FRAME_WIDTH, 1920)
camera.set(cv2.CAP_PROP_FRAME_HEIGHT, 1080)

while(True):
    retval, im = camera.read()
    if im.any(): # errors out when image is none
        cv2.imshow("image", im)

    k = cv2.waitKey(33)
    if k==27: # Esc key press
        print('Resolution: {0}x and {1}y'.format(im.shape[1],im.shape[0]))
        print('FPS: {0}'.format(camera.get(cv2.CAP_PROP_FPS)))
        break

camera.release()
cv2.destroyAllWindows()

Is the DSHOW the correct API to use and is it the only API to use that can change resolution and FPS of a camera stream using opencv? Or is there something else I'm doing incorrectly?

More details about the system.

Ubuntu 18.04.6
python 3.9.5
opencv-python 4.5.2.52

Thank you in advance for the help!

Regards, Tiz

CodePudding user response：

DSHOW (and MSMF) are windows only.

on linux, use V4L, FFMPEG or GSTREAMER

also, please check the return val of capture.set(), not all properties/values will be supported on any given machine