Modifing metadata from existing phAsset seems not working

Question

In my App I want to make it possible, that the user sets an StarRating from 0 to 5 for any Image he has in his PhotoLibrary. My research shows, that there are a couple of ways to get this done:

Save the exif metadata using the new PHPhotoLibrary

Swift: Custom camera save modified metadata with image

Writing a Photo with Metadata using Photokit

Most of these Answers were creating a new Photo. My snippet now looks like this:

let options = PHContentEditingInputRequestOptions()
options.isNetworkAccessAllowed = true

self.requestContentEditingInput(with: options, completionHandler: {
            (contentEditingInput, _) -> Void in

    if contentEditingInput != nil {

        if let url = contentEditingInput!.fullSizeImageURL {
            if let nsurl = url as? NSURL {
                if let imageSource = CGImageSourceCreateWithURL(nsurl, nil) {
                    var imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) as Dictionary?
                    if imageProperties != nil {
                        imageProperties![kCGImagePropertyIPTCStarRating] = rating as AnyObject

                        let imageData = NSMutableData(contentsOf: url)
                        let image = UIImage(contentsOfFile: url.path)

                        let destination = CGImageDestinationCreateWithData(imageData!, CGImageSourceGetType(imageSource)!, 1, nil)

                        CGImageDestinationAddImage(destination!, image!.cgImage!, imageProperties! as CFDictionary)

                        var contentEditingOutput : PHContentEditingOutput? = nil

                        if CGImageDestinationFinalize(destination!) {
                            let archievedData = NSKeyedArchiver.archivedData(withRootObject: rating)
                            let identifier = "com.example.starrating"
                            let adjustmentData = PHAdjustmentData(formatIdentifier: identifier, formatVersion: "1.0", data: archievedData)

                            contentEditingOutput = PHContentEditingOutput(contentEditingInput: contentEditingInput!)
                            contentEditingOutput!.adjustmentData = adjustmentData
                            if imageData!.write(to: contentEditingOutput!.renderedContentURL, atomically: true) {
                                PHPhotoLibrary.shared().performChanges({
                                    let request = PHAssetChangeRequest(for: self)
                                    request.contentEditingOutput = contentEditingOutput
                                }, completionHandler: {
                                    success, error in
                                    if success && error == nil {
                                        completion(true)
                                    } else {
                                        completion(false)
                                    }
                                })
                            }
                        } else {
                            completion(false)
                        }

                    }
                }
            }
        }
    }
})

Now when I want to read the metadata from the PHAsset I request the ContentEditingInput again and do the following:

if let url = contentEditingInput!.fullSizeImageURL {
    if let nsurl = url as? NSURL {
        if let imageSource = CGImageSourceCreateWithURL(nsurl, nil) {
            if let imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) as Dictionary? {

                if let starRating = imageProperties[kCGImagePropertyIPTCStarRating] as? Int {
                    rating = starRating
                }
            }
        }
    }
}

But I never get my rating because it says that the value of imageProperties[kCGImagePropertyIPTCStarRating] is nil.

I also tried the examples from the Answers I posted above, but I always get the same result.

I hope anybody knows, what I can do to change the Metadata.

Also, how can I change the Metadata from an PHAsset with the MediaType .video? I tried to achieve that through the AVAssetWriter and AVExportSession Objects, but in both cases it does not work. Here what I tried for Videos:

var exportSession = AVAssetExportSession(asset: asset!, presetName: AVAssetExportPresetPassthrough)
exportSession!.outputURL = outputURL
exportSession!.outputFileType = AVFileTypeQuickTimeMovie
exportSession!.timeRange = CMTimeRange(start: start, duration: duration)

var modifiedMetadata = asset!.metadata

let metadataItem = AVMutableMetadataItem()
metadataItem.keySpace = AVMetadataKeySpaceQuickTimeMetadata
metadataItem.key = AVMetadataQuickTimeMetadataKeyRatingUser as NSCopying & NSObjectProtocol
metadataItem.value = rating as NSCopying & NSObjectProtocol

modifiedMetadata.append(metadataItem)

exportSession!.metadata = modifiedMetadata


exportSession!.exportAsynchronously(completionHandler: {
    let status = exportSession?.status
    let success = status == AVAssetExportSessionStatus.completed
    if success {
        do {
            let sourceURL = urlAsset.url
            let manager = FileManager.default
            _ = try manager.removeItem(at: sourceURL)
            _ = try manager.moveItem(at: outputURL, to: sourceURL)
        } catch {
            LogError("\(error)")
            completion(false)
        }
    } else {
        LogError("\(exportSession!.error!)")
        completion(false)
    }
})

Answer 1

Sorry this isn't a full answer but it covers one part of your question. I noticed you are placing the StarRating in the wrong place. You need to place it in a IPTC dictionary. Also the properties data is stored as strings. Given you have the imageProperties you can add the star rating as follows and read it back using the following two functions

func setIPTCStarRating(imageProperties : NSMutableDictionary, rating : Int) {
    if let iptc = imageProperties[kCGImagePropertyIPTCDictionary] as? NSMutableDictionary {
        iptc[kCGImagePropertyIPTCStarRating] = String(rating)
    } else {
        let iptc = NSMutableDictionary()
        iptc[kCGImagePropertyIPTCStarRating] = String(rating)
        imageProperties[kCGImagePropertyIPTCDictionary] = iptc
    }
}


func getIPTCStarRating(imageProperties : NSMutableDictionary) -> Int? {
    if let iptc = imageProperties[kCGImagePropertyIPTCDictionary] as? NSDictionary {
        if let starRating = iptc[kCGImagePropertyIPTCStarRating] as? String {
            return Int(starRating)
        }
    }
    return nil
}

As the imageProperties you get from the image are not mutable you need to create a mutable copy of these properties first before you can call the functions above. When you create your image to save use the mutable properties in your call to CGImageDestinationAddImage()

if let mutableProperties = imageProperties.mutableCopy() as? NSMutableDictionary {
    setIPTCStarRating(imageProperties:mutableProperties, rating:rating)
}

One other point you are creating an unnecessary UIImage. If you use CGImageDestinationAddImageFromSource() instead of CGImageDestinationAddImage() you can use the imageSource you created earlier instead of loading the image data into a UIImage.