Lottie is a Animation file based on JSON format. Lottie files in JSON format takes minimal space in comparison to a GIF file or a PNG File. You can convert existing Logo in PNG format to  Lottie JSON file using After Effects or if you are not too tech savvy, you can use Lottie File Marketplace or Fiverr. You can also use Existing Files on LottieFiles as long as Credit is given to the creator.