Android Xamarin Video Tablet editing

Create a android tablet application that can take a photo and a video using the built in camera. Generate a single video file that concatenates both the photo and video into one video with the photo as the beginning content for 5 seconds. Use case: User takes a photo called photo1.jpg. User then takes a 10 second video called video.mp4. User taps the next button and it generates a one single final video of length15 seconds with the photo as the first 5 seconds followed by the video that the user took. Android target framework should be API 27. I prefer using the ffmpeg binary but will accept other solutions. Programmer must use Xamarin and c#.