convert_heic01.swift

import Foundation
import AppKit
import AVFoundation

extension NSImage {
    @objc var CGImage: CGImage? {
        get {
            guard let imageData = self.tiffRepresentation else { return nil }
            guard let sourceData = CGImageSourceCreateWithData(imageData as CFData, nil) else { return nil }
            return CGImageSourceCreateImageAtIndex(sourceData, 0, nil)
        }
    }
}

let output = "wallpapers-new/output.heic"
let quality = 0.9
var imageData: Data? = nil

if let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {

    let destinationData = NSMutableData()
    if let destination = CGImageDestinationCreateWithData(destinationData, AVFileType.heic as CFString, 16, nil) {
        let options = [kCGImageDestinationLossyCompressionQuality: quality]

        for index in 1...16 {
            let fileURL = dir.appendingPathComponent("wallpapers-new/\(index).png")
            let orginalImage = NSImage(contentsOf: fileURL)

            if let cgImage = orginalImage?.CGImage {
                    CGImageDestinationAddImage(destination, cgImage, options as CFDictionary)
            }
        }

        CGImageDestinationFinalize(destination)
        imageData = destinationData as Data

        let outputURL = dir.appendingPathComponent(output)
        try! imageData?.write(to: outputURL)
    }
}