guard let videoTrack = videoAsset.tracks(withMediaType: AVMediaTypeVideo).first else { return }
let videoComposition = AVMutableVideoComposition()
videoComposition.frameDuration = CMTimeMake(1, 30)
videoComposition.renderSize = CGSize(width: videoTrack.naturalSize.height, height: videoTrack.naturalSize.height)

let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, videoAsset.duration)

let transformer = AVMutableVideoCompositionLayerInstruction.init(assetTrack: videoTrack)
let t1 = CGAffineTransform(translationX: videoTrack.naturalSize.height, y: 0)
let t2 = CGAffineTransform(rotationAngle: CGFloat(Double.pi / 2))
t1.concatenating(t2)
transformer.setTransform(t1, at: kCMTimeZero)

instruction.layerInstructions = [transformer]
videoComposition.instructions = [instruction]

guard let documentPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true).first else { return }
let exportPath = documentPath + "/" + defineFileName() // THIS IS JUST DEFINE RANDOM NAME
let exportUrl = URL(fileURLWithPath: exportPath)

let exporter = AVAssetExportSession.init(asset: videoAsset, presetName: AVAssetExportPresetHighestQuality)
exporter?.videoComposition = videoComposition
exporter?.outputURL = exportUrl
exporter?.outputFileType = AVFileTypeQuickTimeMovie

exporter?.exportAsynchronously(completionHandler: { () -> Void in
  let library = ALAssetsLibrary()
  if library.videoAtPathIs(compatibleWithSavedPhotosAlbum: exportUrl) {
    library.writeVideoAtPath(toSavedPhotosAlbum: exportUrl, completionBlock: nil)
  }
})