AVAssetExportSession progress not updating - swift

Question

I make use of AVAssetExportSession to export movies to MP4 format using the codes below:
Step 1: User clicks a button to start conversion
#IBAction func clickConvert(_ sender:UIButton) {
self.convertProgress?.progress = 0
self.convertProgress?.isHidden = false
var preset = AVAssetExportPresetHighestQuality
switch self.qualitySelection?.selectedSegmentIndex {
case 0:
preset = AVAssetExportPresetLowQuality
break
case 1:
preset = AVAssetExportPresetMediumQuality
break
case 2:
preset = AVAssetExportPresetHighestQuality
break
default:
break
}
DispatchQueue.global(qos: .background).async {
let formatter = DateFormatter()
formatter.dateFormat = "yyyyMMddHHmmss"
let fileName = formatter.string(from: Date()) + ".mp4"
let convertGroup = DispatchGroup()
convertGroup.enter()
do {
let documentDirectory = try self.fileManager.url(for: .documentDirectory, in: .userDomainMask, appropriateFor:nil, create:false)
let filePath = documentDirectory.appendingPathComponent(fileName)
if(self.videoURL != nil) {
self.convertVideo(fromURL: self.videoURL!, toURL: filePath, preset: preset, dispatchGroup: convertGroup)
} else {
print("nil Video URL")
}
convertGroup.notify(queue: DispatchQueue.main) {
// reset Convert button state
self.convertButton?.titleLabel?.text = "Convert"
self.convertButton?.isEnabled = true
self.delegate?.updateFileList()
// Take back to old VC, update file list
if let navController = self.navigationController {
navController.popViewController(animated: true)
}
}
} catch {
print(error)
}
}
}
Step 2: Trigger convert video function
func convertVideo(fromURL: URL, toURL: URL, preset:String, dispatchGroup: DispatchGroup) {
let outFileType = AVFileType.mp4
let inAsset = AVAsset(url: fromURL)
let startDate = Date()
AVAssetExportSession.determineCompatibility(ofExportPreset: preset, with: inAsset, outputFileType: outFileType, completionHandler: { (isCompitable) in
if !isCompitable {
return
}
guard let export = AVAssetExportSession(asset: inAsset, presetName: preset) else {
return
}
export.outputFileType = outFileType
export.outputURL = toURL
export.shouldOptimizeForNetworkUse = true
let start = CMTimeMakeWithSeconds(0.0, preferredTimescale: 0)
let range = CMTimeRangeMake(start: start, duration: inAsset.duration)
export.timeRange = range
// Timer for progress updates
self.exportTimer = Timer()
if #available(iOS 10.0, *) {
print("start exportTimer")
self.exportTimer = Timer.scheduledTimer(withTimeInterval: 0.05, repeats: true, block: { _ in
let progress = Float(export.progress)
print("Export Progress: \(progress)")
self.updateProgressDisplay(progress: progress)
if progress < 0.99 {
let dict:[String: Float] = ["progress": progress]
NotificationCenter.default.post(name: Notification.Name(Constants.Notifications.ConvertProgress.rawValue), object: nil, userInfo: dict)
}
})
}
export.exportAsynchronously { () -> Void in
// Handle export results
switch export.status {
case .exporting:
print("Exporting...")
self.updateProgressDisplay(progress: export.progress)
break
case .failed:
print("Error: %#!", export.error!)
break
case .cancelled:
print("export cancelled")
break
case .completed:
let endDate = Date()
let elapsed = endDate.timeIntervalSince(startDate)
print("Elapsed: \(elapsed)")
print("successful")
self.exportTimer?.invalidate() // Stop the timer
self.generateThumbnail(path: toURL)
break
default:
break
}
dispatchGroup.leave()
}
})
}
However, status update is not working, as the timer exportTimer never fires (attempt 1), and the exportSession.exporting case never fires (attempt 2).
p.s. The video can be converted without any problem
p.s. the Notification has been added in viewDidLoad() as follow:
NotificationCenter.default.addObserver(self, selector: #selector(onDidReceiveConvertProgress(_:)), name: Notification.Name(Constants.Notifications.ConvertProgress.rawValue), object: nil)
Status update functions (both attempts) are as follow:
#objc func onDidReceiveConvertProgress(_ notification:Notification) {
print ("onDidReceiveConvertProgress")
if let data = notification.userInfo as? [String:Float] {
print("Progress: \(String(describing: data["progress"]))")
self.convertProgress?.progress = data["progress"]!
}
}
func updateProgressDisplay(progress: Float) {
print("updateProgressDisplay")
self.convertProgress?.progress = progress
}
What did I miss?

Answer 1

I'm not sure if you figured this out, but just in case someone else try your code, the problem why the progress timer is not firing is because you missed two things.
You never called the function to start the timer. e.g. self.exportTimer.fire()
You have to make sure to update this timer on the main Queue.
I had the same problems and doing these two things fixed my issue.