Can't open camera using C++ OpenCV on android

Question

I'm trying to move a very simple OpenCV application to android. The code tries to access the camera from a C++ .so library that is linked with the main app which is using C# and Xamarin which I doubt has anything to do with my issue. My C++ code simply tries to access the camera using cv::VideoCapture like so:

    cv::VideoCapture cap(0); //default camera

    if(!cap.isOpened())
    {
        LOGE("No camera detected on this system\n");
    }

This however always fails despite me specifying permission in AndroidManifest.xml like so:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionCode="1" android:versionName="1.0" package="com.companyname.XamarinARapp">
  <uses-sdk android:minSdkVersion="15" />
  <application android:label="XamarinARapp.Android">
  </application>
  <uses-permission android:name="android.permission.CAMERA"/>
  <uses-feature android:name="android.hardware.camera" android:required="false"/>
  <uses-feature android:name="android.hardware.camera.autofocus" android:required="false"/>
  <uses-feature android:name="android.hardware.camera.front" android:required="false"/>
  <uses-feature android:name="android.hardware.camera.front.autofocus" android:required="false"/>
</manifest>

Has anyone been successful accessing the android camera with cv::VideoCapture in C++? Does Xamarin have anything to do with it?

What Android API version are you testing on? i.e. Have you requested runtime camera permission in your code for API level 23+ devices? — SushiHangover
– SushiHangover, Commented Mar 6, 2018 at 19:31
I'm testing on on android 8.0 Nexus 5X but the app is being built for android 4.4 — PgrAm
– PgrAm, Commented Mar 6, 2018 at 20:11
I see a min. target API listed in your manifest.... What about the target? — SushiHangover
– SushiHangover, Commented Mar 6, 2018 at 20:13

SushiHangover · Accepted Answer · 2018-03-06 20:51:11Z

2

but the app is being built for android 4.4

Your manifest SDK versions should look like this:

<uses-sdk android:minSdkVersion="19" android:targetSdkVersion="19" />

Otherwise without the targetSdkVersion set and running on a API 23+ device you will need to request runtime camera permissions.

edited Mar 6, 2018 at 20:51

answered Mar 6, 2018 at 20:20

SushiHangover

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1 Comment

PgrAm Over a year ago

I modified my code to request run-time camera permissions using the Xamarin Plugin.Permissions, and the permissions are definitely being granted, however the issue persists. Changed both minSdkVersion and targetSdkVersion to 24

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