iOS AVFoundation：设置使用面部相机录制的视频方向

Question

func orientationFromTransform(transform: CGAffineTransform) -> (orientation: UIImageOrientation, isPortrait: Bool) {
    print(transform)
    var assetOrientation = UIImageOrientation.up
    var isPortrait = false

    if transform.a == 0 && transform.b == 1.0 && transform.c == -1.0 && transform.d == 0 {
        assetOrientation = .right
        isPortrait = true
    }
    else if transform.a == 0 && transform.b == -1.0 && transform.c == 1.0 && transform.d == 0 {
        assetOrientation = .left
        isPortrait = true
    }
    else if transform.a == 1.0 && transform.b == 0 && transform.c == 0 && transform.d == 1.0 {
        assetOrientation = .up
    }
    else if transform.a == -1.0 && transform.b == 0 && transform.c == 0 && transform.d == -1.0 {
        assetOrientation = .down
    }
    else if transform.a == 0 && transform.b == 1.0 && transform.c == 1.0 && transform.d == 0 {
        isPortrait = true
    }

    return (assetOrientation, isPortrait)

}

func videoCompositionInstructionForTrack(track: AVCompositionTrack, asset: AVAsset) -> AVMutableVideoCompositionLayerInstruction {

    let instruction = AVMutableVideoCompositionLayerInstruction(assetTrack: track)
    let assetTrack = asset.tracks(withMediaType: AVMediaTypeVideo)[0]

    let transform = assetTrack.preferredTransform
    let assetInfo = orientationFromTransform(transform: transform)

    var scaleToFitRatio = UIScreen.main.bounds.width / assetTrack.naturalSize.width
    if assetInfo.isPortrait {
        scaleToFitRatio = UIScreen.main.bounds.width / assetTrack.naturalSize.height
        let scaleFactor = CGAffineTransform(scaleX: scaleToFitRatio, y: scaleToFitRatio)
        instruction.setTransform(assetTrack.preferredTransform.concatenating(scaleFactor),
                             at: kCMTimeZero)
    }
    else {

        let scaleFactor = CGAffineTransform(scaleX: scaleToFitRatio, y: scaleToFitRatio)
        var concat = assetTrack.preferredTransform.concatenating(scaleFactor).concatenating(CGAffineTransform(translationX: 0, y: UIScreen.main.bounds.width / 2))

        if assetInfo.orientation == .down {

            let fixUpsideDown = CGAffineTransform(rotationAngle: CGFloat(M_PI))
            let windowBounds = UIScreen.main.bounds
            let yFix = assetTrack.naturalSize.height + windowBounds.height
            let centerFix = CGAffineTransform(translationX: assetTrack.naturalSize.width, y: yFix)
            concat = fixUpsideDown.concatenating(centerFix).concatenating(scaleFactor)

        }

        instruction.setTransform(concat, at: kCMTimeZero)

    }

    return instruction

}

func mergeVideos(sourceVideos: [URL], completion: @escaping (_ outputURL: URL, _ success: Bool) -> Void) {

    let composition = AVMutableComposition()
    let track = composition.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID:Int32(kCMPersistentTrackID_Invalid))

    var duration = kCMTimeZero
    var instructions = [AVVideoCompositionLayerInstruction]()

    for url in sourceVideos {

        let videoAsset = AVURLAsset(url: url)

        if url == sourceVideos.first {
            do {
                try track.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), of: videoAsset.tracks(withMediaType: AVMediaTypeVideo)[0], at: kCMTimeZero)
            }
            catch {
                completion(URL(string: "")!, false)
            }
        }
        else {
            do {
                try track.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), of: videoAsset.tracks(withMediaType: AVMediaTypeVideo)[0], at: composition.duration)
            }
            catch {
                completion(URL(string: "")!, false)
            }
        }

        duration = CMTimeAdd(duration, videoAsset.duration)
        instructions.append(videoCompositionInstructionForTrack(track: track, asset: videoAsset))

    }

    let mainInstruction = AVMutableVideoCompositionInstruction()
    mainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, duration)
    mainInstruction.layerInstructions = instructions

    let mainComposition = AVMutableVideoComposition()
    mainComposition.instructions = [mainInstruction]
    mainComposition.frameDuration = CMTimeMake(1, 60)
    mainComposition.renderSize = CGSize(width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height)

    var paths = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)
    let documentsDirectory = paths[0] as String
    let videoPathToSave = documentsDirectory.stringByAppendingPathComponent(path: "mergeVideo-\(arc4random()%1000)-d.mov")
    let videoURLToSave = NSURL(fileURLWithPath: videoPathToSave)

    guard let exporter = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetHighestQuality) else {
        completion(URL(string: "")!, false)
        return
    }
    exporter.outputURL = videoURLToSave as URL
    exporter.videoComposition = mainComposition
    exporter.outputFileType = AVFileTypeQuickTimeMovie
    exporter.shouldOptimizeForNetworkUse = true
    exporter.exportAsynchronously {
        DispatchQueue.main.async {
            for url in sourceVideos {
                do {
                    try FileManager.default.removeItem(at: url)
                }
                catch {}
            }

            completion(exporter.outputURL!, true)
        }
    }

}

此代码适用于后置摄像头，但如果使用面部摄像头录制，则显示错误的缩放。这段代码是我从以下链接考虑的。

https://www.raywenderlich.com/94404/play-record-merge-videos-ios-swift

我真的想知道如何修复脸部相机的方向......

enter image description here