Create openCV VideoCapture from interface name instead of camera numbers

Question

The normal way to create a videocapture is this:

cam = cv2.VideoCapture(n)

where n corresponds to the number of /dev/video0,

Answer 1

import re
import subprocess
import cv2
import os

device_re = re.compile("Bus\s+(?P\d+)\s+Device\s+(?P\d+).+ID\s(?P\w+:\w+)\s(?P.+)$", re.I)
df = subprocess.check_output("lsusb", shell=True)
for i in df.split('\n'):
    if i:
        info = device_re.match(i)
        if info:
            dinfo = info.groupdict()
            if "Logitech, Inc. Webcam C270" in dinfo['tag']:
                print "Camera found."
                bus = dinfo['bus']
                device = dinfo['device']
                break

device_index = None
for file in os.listdir("/sys/class/video4linux"):
    real_file = os.path.realpath("/sys/class/video4linux/" + file)
    print real_file
    print "/" + str(bus[-1]) + "-" + str(device[-1]) + "/"
    if "/" + str(bus[-1]) + "-" + str(device[-1]) + "/" in real_file:
        device_index = real_file[-1]
        print "Hurray, device index is " + str(device_index)


camera = cv2.VideoCapture(int(device_index))

while True:
    (grabbed, frame) = camera.read() # Grab the first frame
    cv2.imshow("Camera", frame)
    key = cv2.waitKey(1) & 0xFF

First search for desired string in USB devices list. Get BUS and DEVICE number.

Find symbolic link under video4linux directory. Extract device index from realpath and pass it to VideoCapture method.