How to approach building a live moveable video crop?

So say you have a bird flying from left to right side of screen of a video and you want to crop a 4:3 box around the bird that follows it from left to right so in the end you get a 4:3 video with the bird centered in frame but cropped in and 4:3. Yes this can be done through key framing but I want to build an intuitive UI that allows you to simply drag the cropped box where you want it to be while the video is playing.

Is there any existing code that I can use to build this or os this going to have to be made from scratch. I’m thinking some sort of cropped screen recording or something?