Build me a Video editor (Video Merger) for an Android Application using Android Studio

I'm working on an android social media app that makes use of video merging. I need a simple function, it must merge videos selected/taken by the user together that creates a new video which can then be saved to the device. What it must be able to do: -Users are able to select videos from their gallery on the application -Users are also able to take videos using the application using the devices camera -Users are then able to merge videos they have selected, creating a new video -They can unselect any videos they might not want. -Users can preview the new video they have made on the application -Users are then able to save this new video they have made to their device Must be done in Java, you'll be working on an existing project by adding to it - you can make any changes as you want as long as the function works in the end.