Camera frames in a service / background process

Question

For scientific measurements, I would like to access the camera frames from a service. The idea is to analyze the images coming from the camera in real-time under some condit

Answer 1

I use this code my Spy Application for Live camera stream. (This for Xamarin, convert it to Java)

Firstly add permission:

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

Put this code into the your Foreground Service. With this code, SurfaceView works independently from Lifecycle of Activity

public void CamInService()
        {
            var layoutParams = new ViewGroup.LayoutParams(100, 100);
            var view = new SurfaceView(this)
            {
                LayoutParameters = layoutParams
            };
            view.Holder.AddCallback(new Prev()); //Replace with your preview callback
            WindowManagerLayoutParams winparam = new WindowManagerLayoutParams(WindowManagerTypes.SystemAlert);
            winparam.Flags = WindowManagerFlags.NotTouchModal;
            winparam.Flags |= WindowManagerFlags.NotFocusable;
            winparam.Format = Android.Graphics.Format.Rgba8888;
            winparam.Width = 1;
            winparam.Height = 1;

            IWindowManager windowManager = GetSystemService(WindowService).JavaCast<IWindowManager>();
            windowManager.AddView(view, winparam);
        }  

and call this method in OnCreate() method of Service or anywhere in the Application. For access from anywhere declare a variable in your foreground service class like this: public static ForegroundService _globalService; and access from anywhere like this: ForegroundService._globalService.CamInService();

Note: replace "ForegroundService" word with your Service class name.

Answer 2

You can send the preview to a SurfaceTexture instead (setPreviewTexture()). This won't disappear when the app is paused. Requires API 11+.

You can see various applications of this technique in Grafika, which is generally doing video or GLES manipulation rather than stills, but the idea is similar.