How to write AVMetaDateItem to a file and accessing it later?

Question

I wrought this function to trim a specific part of an audio file. In the function, I'm writing to the new file two AVMetadataItems. I was trying to access these items later by rapping the URL with AvURlAsset and then accessing the AVAsset metaData /commonMetadata and both didn't contain the item I added before.

So I checked what happens before I'm exporting the file, and even though I gave exporter.metadata an array oh AVMetadataitem, its still appears to be nil before the exportation.

any one knows what is the problem?

func trimFromOffSetWithDuration(_ from: Date, startOffSet: TimeInterval, duration: TimeInterval, newfileName: String, file: URL, completion: fileExportaionBlock?) {

    if let asset = AVURLAsset(url: file) as AVAsset? {

        let trimmedFileUrl = documentsDirectory().appendingPathComponent(newfileName)

        let exporter = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetAppleM4A)
        exporter?.outputFileType = AVFileTypeAppleM4A
        exporter?.outputURL = trimmedFileUrl

        let start = CMTimeMake(Int64(startOffSet), 1)
        let end = CMTimeMake(Int64(startOffSet + duration), 1)
        exporter?.timeRange = CMTimeRangeFromTimeToTime(start, end)

        let typeMetaDataItem = AVMutableMetadataItem()
        typeMetaDataItem.key = AVMetadataCommonKeyDescription as  NSCopying & NSObjectProtocol
        typeMetaDataItem.keySpace = AVMetadataKeySpaceCommon
        typeMetaDataItem.value = TrackType.recording.rawValue as NSCopying & NSObjectProtocol

        let dateMetaDataItem = AVMutableMetadataItem()
        dateMetaDataItem.key = AVMetadataCommonKeyCreationDate as NSCopying & NSObjectProtocol
        dateMetaDataItem.keySpace = AVMetadataKeySpaceCommon
        dateMetaDataItem.value = from as NSCopying & NSObjectProtocol

        exporter?.metadata? = [dateMetaDataItem, typeMetaDataItem]
        exporter?.exportAsynchronously { handler in

            if exporter?.status != AVAssetExportSessionStatus.completed {
                print("Error while exporting \(exporter?.error?.localizedDescription ?? "unknown")")
                completion?(nil)
                return
            }
        }

        completion?(trimmedFileUrl)
    }
}

Answer 1

You should move completion?(trimmedFileUrl) inside the completion block of exportAsynchronously.