Add overlay to captured image and recorded videos in Android CameraX

In my project I need to overlay a captured picture or a recorded video with some sensor values in Android CameraX (Beta). Overlaying the preview works fine but I also need to overlay the values when I'm recording or capturing. I know that recording videos is still a restricted use case in cameraX at the moment but I'd already be happy to add the overlay to the captured images. Looking at the docs and the posts I dont't have any idea where to start. Maybe someone can give me some hints where to start with the developement!