How can I add a layer (layer) to a video file with its dynamic information?

Question

iOS

Good afternoon. I'm developing an application and I've run into a problem. I have the final video file. Which is recorded by the device's camera. I need to apply dynamic information to it. For example, this would be a real-time date. How can I add a layer to the final video file that will contain the given date and at the same time receive a glued final video file.