What is a live photo file?

UTType.swift

import Foundation
import MobileCoreServices


if let t = UTTypeCreateAllIdentifiersForTag(kUTTagClassFilenameExtension, "mp4" as CFString, nil)?.takeRetainedValue() as? [CFString] {
    print(t)
    print(UTTypeConformsTo(t[0], kUTTypeMovie), "\n")
}

if let t = UTTypeCreateAllIdentifiersForTag(kUTTagClassMIMEType, "application/json" as CFString, nil)?.takeRetainedValue() as? [CFString] {
    print(t)
    print(UTTypeConformsTo(t[0], kUTTypeText), "\n")
}

if let t = UTTypeCopyPreferredTagWithClass(kUTTypeJPEG, kUTTagClassFilenameExtension)?.takeRetainedValue() {
    print(t, "\n")
}

for uti in [kUTTypeJPEG, kUTTypeLivePhoto, kUTTypeMPEG, kUTTypeMPEG4, kUTTypePDF, kUTTypeJSON] {
    if let d = UTTypeCopyDescription(uti)?.takeRetainedValue() {
        print(d)
    }
    if let d = UTTypeCopyDeclaration(uti)?.takeRetainedValue() as? [String : Any] {
        print(d)
    }
    print()
}

// kUTTypeLivePhoto has no file extension, and conforms to nobody
// https://stackoverflow.com/questions/32508375/apple-live-photo-file-format
// It contains both a JPEG and a quicktime MOV
print(UTTypeConformsTo(kUTTypeLivePhoto, kUTTypeImage)) // false

关于 UTI（Uniform Type Identifiers），还有一篇文章的介绍比官方更好，
https://arstechnica.com/gadgets/2005/04/macosx-10-4/11/