AVURLAsset reverting to original orientation even though the video file is mirrored - swift

Question

I am trying to merge videos that are recorded to local files. I want to support both the front and back camera but saw that recording with the front camera causes the video to flip. So when recording I used...
func startRecording(){
if isCameraButtonDisabled == false {
// MARK: Temporary URL for recording Video
let tempURL = NSTemporaryDirectory() + "\(Date()).mov"
if self.videoDeviceInput.device.position == .back {
output.startRecording(to: URL(fileURLWithPath: tempURL), recordingDelegate: self)
} else {
output.connection(with: AVMediaType.video)?.isVideoMirrored = true
output.startRecording(to: URL(fileURLWithPath: tempURL), recordingDelegate: self)
}
withAnimation(.spring(response: 0.5, dampingFraction: 0.5, blendDuration: 1)) {
isRecording = true
}
}
}
However, when I return only the outputFileURL the front-facing video is mirrored as I intended. But after I convert each video into an AVURLAsset for the purpose of combining the videos, it changes the orientation of the video back to the original (non-mirrored) version. I am very confused as to why this happens and how I can maintain the mirrored version when joining videos using AVURLAsset. Here is the function that returns the video file as well as the one that merges them.
func fileOutput(_ output: AVCaptureFileOutput, didFinishRecordingTo outputFileURL: URL, from connections: [AVCaptureConnection], error: Error?) {
if let error = error {
print(error.localizedDescription)
return
}
withAnimation {
self.recordedURLs.append(outputFileURL)
}
if self.recordedURLs.count == 1{
self.previewURL = outputFileURL
return
}
let assets = recordedURLs.compactMap { url -> AVURLAsset in
return AVURLAsset(url: url)
}
for asset in assets {
print(asset.preferredTransform)
}
self.previewURL = nil
mergeVideos(assets: assets) { exporter in
exporter.exportAsynchronously {
if exporter.status == .failed{
// HANDLE ERROR
print(exporter.error!)
}
else{
if let finalURL = exporter.outputURL{
print(finalURL)
DispatchQueue.main.async {
self.previewURL = finalURL
}
}
}
}
}
}
func mergeVideos(assets: [AVURLAsset],completion: #escaping (_ exporter: AVAssetExportSession)->()){
let compostion = AVMutableComposition()
var lastTime: CMTime = .zero
guard let videoTrack = compostion.addMutableTrack(withMediaType: .video, preferredTrackID: Int32(kCMPersistentTrackID_Invalid)) else{return}
guard let audioTrack = compostion.addMutableTrack(withMediaType: .audio, preferredTrackID: Int32(kCMPersistentTrackID_Invalid)) else{return}
for asset in assets {
// Linking Audio and Video
do{
try videoTrack.insertTimeRange(CMTimeRange(start: .zero, duration: asset.duration), of: asset.tracks(withMediaType: .video)[0], at: lastTime)
// Safe Check if Video has Audio
if !asset.tracks(withMediaType: .audio).isEmpty{
try audioTrack.insertTimeRange(CMTimeRange(start: .zero, duration: asset.duration), of: asset.tracks(withMediaType: .audio)[0], at: lastTime)
}
}
catch{
print(error.localizedDescription)
}
lastTime = CMTimeAdd(lastTime, asset.duration)
}
// MARK: Temp Output URL
let tempURL = URL(fileURLWithPath: NSTemporaryDirectory() + "\(Date()).mp4")
let layerInstructions = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
var transform = CGAffineTransform.identity
transform = transform.rotated(by: 90 * (.pi / 180))//
transform = transform.translatedBy(x: 0, y: -videoTrack.naturalSize.height)//
layerInstructions.setTransform(transform, at: .zero)
let instructions = AVMutableVideoCompositionInstruction()
instructions.timeRange = CMTimeRange(start: .zero, duration: lastTime)
instructions.layerInstructions = [layerInstructions]
let videoComposition = AVMutableVideoComposition()
videoComposition.renderSize = CGSize(width: videoTrack.naturalSize.height, height: videoTrack.naturalSize.width)
videoComposition.instructions = [instructions]
videoComposition.frameDuration = CMTimeMake(value: 1, timescale: 30)
guard let exporter = AVAssetExportSession(asset: compostion, presetName: AVAssetExportPresetHighestQuality) else{return}
exporter.outputFileType = .mp4
exporter.outputURL = tempURL
exporter.videoComposition = videoComposition
completion(exporter)
}