ConvertToHEIC

ConvertToHEIC.swift

#!/usr/bin/env swift
//
//  ConvertToHEIC.swift
//  ConvertToHEIC
//
//  Created by Sinoru on 2018. 4. 28..
//

import Foundation
import ImageIO
import AVFoundation

for argument in CommandLine.arguments.dropFirst() {
    print("Converting \(argument).")

    let sourceFileURL = URL(fileURLWithPath: argument)

    guard let imageSource = CGImageSourceCreateWithURL(sourceFileURL as CFURL, nil) else {
        print("Can't not load \(sourceFileURL). Skip")
        continue
    }

    let imageProperties = CGImageSourceCopyProperties(imageSource, nil)
    let imageCount = CGImageSourceGetCount(imageSource)

    let destinationFileURL = sourceFileURL.deletingPathExtension().appendingPathExtension("heic")

    guard let imageDestination = CGImageDestinationCreateWithURL(destinationFileURL as CFURL, AVFileType.heic as CFString, imageCount, nil) else {
        print("Can't not write \(destinationFileURL). Skip")
        continue
    }

    CGImageDestinationSetProperties(imageDestination, imageProperties)
    for index in 0..<imageCount {
        CGImageDestinationAddImageFromSource(imageDestination, imageSource, index, [kCGImageDestinationLossyCompressionQuality: 0.8] as CFDictionary)
    }

    guard CGImageDestinationFinalize(imageDestination) else {
        print("Can't not finalize \(destinationFileURL). Skip")
        continue
    }
}

Thanks for sharing the code. It helps a lot.
For those who have not installed Xcode, I transpiled this swift code into JXA(JavaScript for Automation).
ConvertToHEIC.js

Thank you both! This is a huge help so I can encode my digital camera photos as HEIC before importing to iCloud Photos and save a lot of space.

I cleaned up (and colorized) the output a bit (Swift, JavaScript) just for my own personal photo-management scripts.