func main() {
	flag.Parse()
	...
  
	fin, fout := flag.Arg(0), flag.Arg(1)
	fi, err := os.Open(fin)
	if err != nil {
		log.Fatal(err)
	}
	defer fi.Close()

	exif, err := goheif.ExtractExif(fi)
	if err != nil {
		log.Printf("Warning: no EXIF from %s: %v\n", fin, err)
	}

	img, err := goheif.DecodeImage(fi)
	if err != nil {
		log.Fatalf("Failed to parse %s: %v\n", fin, err)
	}

	fo, err := os.OpenFile(fout, os.O_RDWR|os.O_CREATE, 0644)
	if err != nil {
		log.Fatalf("Failed to create output file %s: %v\n", fout, err)
	}
	defer fo.Close()

	w, _ := newWriterExif(fo, exif)
	err = jpeg.Encode(w, img, nil)
	if err != nil {
		log.Fatalf("Failed to encode %s: %v\n", fout, err)
	}

	log.Printf("Convert %s to %s successfully\n", fin, fout)
}