How i will setup ratio in video swift?

var composition = AVMutableComposition()
let vidtrack = composition.tracks(withMediaType: .video)[0]
let sz = vidtrack.naturalSize

//set ration here
let rect = AVMakeRect(aspectRatio: CGSize(width: 16, height: 9), insideRect: CGRect(origin: .zero, size: CGSize(width: sz.width, height: sz.height)))

• Facebook: 16:9 or 9:16 (max upload 4k - 3840 x 2160)
• Instagram: 16:9 or 9:16 (max upload 1080p)
• Twitter: 16:9 (max upload 1080p)
• Snapchat: 9:16 (1080 x 1920)
• YouTube: 16:9 (max upload 4k - 3840 x 2160)