need app with source code for changing pitch and tempo of a video file mp4

I am looking for a developer to create an app for me with source code that can change the pitch and tempo of a video file (.mp4). My desired platform is Windows and I am open to suggestions for any additional features, although the primary goal is the ability to manipulate the pitch and tempo. I am not particular about the programming language used, but it must be robust and reliable yet simple enough to enable manipulation of both tempo and pitch. If you have a knack for creative app development, don't hesitate to show off your skills and impress me with your creative ideas regarding the design and functionality of the app. This project has the potential to be big, and I am excited to see what you can do!