Test APP for Rooted Phones (Android) - Camera driver

I need to develop a private android app to simply change the route destination of the mobile camera. Basically I just need to route the command: <uses-feature android:name="[login to view URL]" android:required="true" /> Every app that requires a selfie, will open the mobile front camera in order to take pictures. Instead I want to load a file (picture or video) and do not access the camera hardware itself. This way the app will get an image of a picture or video and then I can shot this pre loaded picture using the mobile camera. In case of video, it will continuasly repeat the video. The app should have a feature that will make it on or off, when on it will load a specific file, when off it will use the camera normally. Root access is okay. You can use any aleatory apk package name, to make it easy to hide. The apk that request the camera use, should know that they are actually accesing the mobile camera and using it normally. I dont want to select between the original camera and the fake camera app when requested. If the app is turned on, it will automatically load the pre loaded file to take shots of it. That's it. As simple as possible. No special design needed, as it is not for commercial use. The device we use as test is the Motorola G5 Plus XT1687 Android 7.0.