OpenCV with multiple webcams - how to tell which camera is which in code?

Question

Previously I\'ve used industrial cameras with Ethernet connections and distinct IP addresses for multiple camera setups. Now I\'m attempting a multiple camera setup with Op

Answer 1

For the solution you found, you need root privileges. On my setup with Ubuntu20 this is not required for:

udevadm info --name=/dev/video0

This outputs properties of first camera detected. Pipe it through "grep" to filter out specific property that is different for all cameras like "ID_SERIAL=". You can then use "cut" to remove beginning of this string "ID_SERIAL=" and leave just the value like:

udevadm info --name=/dev/video0 | grep ID_SERIAL= | cut -d "=" -f 2

In Python you can run external command to get this info like:

def get_cam_serial(cam_id):
    # Prepare the external command to extract serial number. 
    p = subprocess.Popen('udevadm info --name=/dev/video{} | grep ID_SERIAL= | cut -d "=" -f 2'.format(cam_id),
                         stdout=subprocess.PIPE, shell=True)

    # Run the command
    (output, err) = p.communicate()

    # Wait for it to finish
    p.status = p.wait()

    # Decode the output
    response = output.decode('utf-8')

    # The response ends with a new line so remove it
    return response.replace('\n', '')

To acquire all the camera serial numbers, just loop through several camera ID's. On my setup trying camera ID 0 and 1 target the same camera. Also 2 and 4 target the second camera, so the loop can have 2 for step. Once all ID's are extracted, place them in a dictionary to be able to associate cam ID with serial number. The complete code could be:

serials = {}
FILTER = "ID_SERIAL="


def get_cam_serial(cam_id):
    p = subprocess.Popen('udevadm info --name=/dev/video{} | grep {} | cut -d "=" -f 2'.format(cam_id, FILTER),
                         stdout=subprocess.PIPE, shell=True)
    (output, err) = p.communicate()
    p.status = p.wait()
    response = output.decode('utf-8')
    return response.replace('\n', '')


for cam_id in range(0, 10, 2):
    serial = get_cam_serial(cam_id)
    if len(serial) > 6:
        serials[cam_id] = serial

print('Serial numbers:', serials)