Create openCV VideoCapture from interface name instead of camera numbers
Each of my video4linux devices creates 2 device nodes. For example, /dev/video0
and /dev/video1
are both related to my internal webcam. When I plug in a second USB webcam, /dev/video2
and /dev/video3
both appear. However, I can only use the lower-numbered device of each pair for video capture (i.e. /dev/video0
and /dev/video2
).
I watched my device arrival with udevadm monitor
, and then inspected each of the camera devices with udevadm info --path=$PATH_FROM_UDEVADM_MONITOR --attribute-walk
. The devices which work for video capture have ATTR{index}=="0"
.
Maybe instead of trying to open /dev/video1
, you just need to open /dev/video0
:
cam = cv2.CaptureVideo("/dev/video0")
import re
import subprocess
import cv2
import os
device_re = re.compile("Bus\s+(?P<bus>\d+)\s+Device\s+(?P<device>\d+).+ID\s(?P<id>\w+:\w+)\s(?P<tag>.+)$", 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.
If you know the model of the camera, you can look it up in /dev/v4l/by-id/...
. We are using an HDMI-USB video converter, and we connect to it like this:
#! /usr/bin/env python
import os
import re
import cv2
DEFAULT_CAMERA_NAME = '/dev/v4l/by-id/usb-AVerMedia_Technologies__Inc._Live_Gamer_Portable_2_Plus_5500114600612-video-index0'
device_num = 0
if os.path.exists(DEFAULT_CAMERA_NAME):
device_path = os.path.realpath(DEFAULT_CAMERA_NAME)
device_re = re.compile("\/dev\/video(\d+)")
info = device_re.match(device_path)
if info:
device_num = int(info.group(1))
print("Using default video capture device on /dev/video" + str(device_num))
cap = cv2.VideoCapture(device_num)
This follows the device name symlink to the /dev/video
name, then parses that for the device number.
Instead of the suggested solution I found a shorter one, that feels a little bit hacky.
I just look at where the symbolic link points, find the integer in it, and then use that.
import subprocess
cmd = "readlink -f /dev/CAMC"
process = subprocess.Popen(cmd.split(), stdout=subprocess.PIPE)
# output of form /dev/videoX
out = process.communicate()[0]
# parse for ints
nums = [int(x) for x in out if x.isdigit()]
cap = cv2.VideoCapture(nums[0])