OpenCV how to select which camera to connect to? - linux

Question

I am writing an OpenCV 3.4 app on Ubuntu 16.04.
However, I am running into a problem where no matter what deviceId I set on my VideoCapture() function, I always get the built in webcam stream. However I need to get the stream from my usb camera. Btw my usb camera is a Logitech c920, and my computer is a ThinkPad P51 (not sure if that would matter)
Here is my code:
#include <opencv2/highgui.hpp>
#include <opencv2/opencv.hpp>
#include <opencv2/aruco.hpp>
#include <iostream>
int main(int, char**){
cv::Mat inputImage;
std::vector<int> markerIds;
std::vector<std::vector<cv::Point2f> > markerCorners, rejectedCandidates;
cv::aruco::DetectorParameters parameters;
cv::VideoCapture inputVideo(1); // I have tried 0, 1, 2...20 all the same stream
cv::Ptr<cv::aruco::Dictionary> dictionary = cv::aruco::getPredefinedDictionary(cv::aruco::DICT_4X4_50);
while (inputVideo.grab()){
cv::Mat image, imageCopy;
inputVideo.retrieve(image);
image.copyTo(imageCopy);
std::vector<int> ids;
std::vector<std::vector<cv::Point2f> > corners;
cv::aruco::detectMarkers(image, dictionary, corners, ids);
if (ids.size() > 0) cv::aruco::drawDetectedMarkers(imageCopy, corners, ids);
cv::imshow("out", imageCopy);
if(cv::waitKey(30) >= 0) break;
}
}
Thanks!
EDIT:
This is the result I get with ls -lR /dev/v4l:
/dev/v4l:
total 0
drwxr-xr-x 2 root root 80 Feb 23 10:53 by-id
drwxr-xr-x 2 root root 80 Feb 23 10:53 by-path
/dev/v4l/by-id:
total 0
lrwxrwxrwx 1 root root 12 Feb 23 10:53 usb-046d_HD_Pro_Webcam_C920_25CCF0FF-video-index0 -> ../../video1
lrwxrwxrwx 1 root root 12 Feb 23 2019 usb-8SSC20F27019L1GZ83C07ZY_Integrated_Camera-video-index0 -> ../../video0
/dev/v4l/by-path:
total 0
lrwxrwxrwx 1 root root 12 Feb 23 10:53 pci-0000:00:14.0-usb-0:6:1.0-video-index0 -> ../../video1
lrwxrwxrwx 1 root root 12 Feb 23 2019 pci-0000:00:14.0-usb-0:8:1.0-video-index0 -> ../../video0
And this is what I get with lsusb:
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 005: ID 138a:0097 Validity Sensors, Inc.
Bus 001 Device 004: ID 04ca:7066 Lite-On Technology Corp.
Bus 001 Device 008: ID 046d:082d Logitech, Inc. HD Pro Webcam C920
Bus 001 Device 003: ID 046d:c539 Logitech, Inc.
Bus 001 Device 002: ID 04d9:0169 Holtek Semiconductor, Inc.
Bus 001 Device 006: ID 8087:0a2b Intel Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Not sure how to match them?