Listing available devices in python-opencv

Question

I have two webcams attached to my laptop (one built in), both of which work. (If I use Cheese, a webcam thingy that comes with Ubuntu, it uses the external one). If I use

Answer 1

I have been able to work around this problem by iterating over the webcam indexes until reading that camera no longer returns anything:

index = 0
arr = []
while True:
    cap = cv2.VideoCapture(index)
    if not cap.read()[0]:
        break
    else:
        arr.append(index)
    cap.release()
    index += 1
return arr

This method returns a list of all indexes that return something when read; I'm sure it can be improved upon, but there are hardly ever more than a few webcams and this runs pretty quickly.

Answer 2

I think you should try this:

import cv2

cap = cv2.VideoCapture(1)

while True:
    _, frame = cap.read()
    cv2.imshow('frame', frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

Answer 3

I believe that under Linux the valid indices for video inputs are the numbers of the videoN devices in the /dev directory. Hence the following will give a list of valid indices:

import os
devs = os.listdir('/dev')
vid_indices = [int(dev[-1]) for dev in devs 
               if dev.startswith('video')]
vid_indices = sorted(vid_indices)
vid_indices

Answer 4

This is a general problem of the OpenCV, as you can see below. It seems that only the builtin, or the first USB cam (only if you do not have a buildin cam) works in OpenCV:

How to use a camera with OpenCV

Cannot access usb webcam through OpenCV, Cygwin

OpenCV capture from USB not iSight (OSX)

Currently, there is no way to extract the number of cameras, as listed in this feature request:

https://code.ros.org/trac/opencv/ticket/935

Answer 5

Great answer by @Patrick, but I'd like to improve on it and can't comment yet.

I think Patricks setup assumes that the cameras do not have empty indexes in between them. But in my case, my built-in camera was at index 0, and USB webcam was at index 2. So "if not cap.read()[0]" broke out of the while loop at index 1, never catching the others. We have to specify how many indexes we're willing to go over and check, and just not add the ones that are null.

def returnCameraIndexes():
    # checks the first 10 indexes.
    index = 0
    arr = []
    i = 10
    while i > 0:
        cap = cv2.VideoCapture(index)
        if cap.read()[0]:
            arr.append(index)
            cap.release()
        index += 1
        i -= 1
    return arr

This successfully gave me the indexes I need. Again, thanks to Patrick for the layout!

Answer 6

For windows, you can build a .pyd extension. https://github.com/yushulx/python-capture-device-list

There isn't an easy crossplatform way yet; ideally someone collates a solution for each OS and then builds them into .pyd.