UWP app video processing update C++

I have made a UWP app in C# (Visual Studio 2019) which records 4 separate webcam videos and plays them back in sync. See this video for the basic functionality: [login to view URL] Another coder made a working C++ library which renders the 4 videos into one 4:3 .wmv file. I need assistance to update the C++ library to work with 16:9 and 4:3 aspect ratios and produce a new .mp4 video. The previous code is all working, just not with 16:9 format for some reason. I also want to integrate an in-app purchase for this 'mixdown' functionality. Most of the code is already written and working, so the project shouldn't be too hard for someone that knows what they're doing with C++ and low-level video operations (not me :). I've also got most of the recommended C# functions for in-app purchase in the app already which should save time for someone who has done this before (not me :). Please include a ":)" at the beginning of your reply so I know you have read this far, thanks. The code is available on bitbucket or I can send the solution files.