AVAssetTrack理解preferredTransform属性

Question

我面对AVAssetTrack的preferredTransform属性的误解。在我的应用程序中，我正在提取视频帧并尝试显示它们，但我不了解帧数据的布局方式以及preferredTransform属性的含义（如果必须将此转换应用于帧数据，那么图像必须可以正确显示，但根本不可见；如果此变换已应用到图像，则过度使用必须将图像恢复为正常状态，但它也不起作用。

在一些教程中，我看到了这段代码来修复转换

extension AVAssetTrack {
    var orientation: (orientation: UIImage.Orientation, isPortrait: Bool) {
        let transform = self.preferredTransform

        var assetOrientation = UIImage.Orientation.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
        }
        return (assetOrientation, isPortrait)
    }

    var fixedVideoTransform: CGAffineTransform {


        let videoOrientation = self.orientation

        var resultTransform = CGAffineTransform.identity

        // Now we need fully discard all video transforms and show video as it was in preview
        switch videoOrientation.orientation {
        case .down:
            let rotationFix = CGAffineTransform.identity.translatedBy(x: videoAssetTrack.naturalSize.width - videoAssetTrack.preferredTransform.tx, y: videoAssetTrack.naturalSize.height - videoAssetTrack.preferredTransform.ty)
            resultTransform = videoAssetTrack.preferredTransform.concatenating(rotationFix)

        case .right:
            let rotationFix = CGAffineTransform.identity.translatedBy(x: videoAssetTrack.naturalSize.height - videoAssetTrack.preferredTransform.tx, y: -videoAssetTrack.preferredTransform.ty)
            resultTransform = videoAssetTrack.preferredTransform.concatenating(rotationFix)

        case .left:
            let rotationFix = CGAffineTransform.identity.translatedBy(x:  -videoAssetTrack.preferredTransform.tx, y: videoAssetTrack.naturalSize.width - videoAssetTrack.preferredTransform.ty)
            resultTransform = videoAssetTrack.preferredTransform.concatenating(rotationFix)


        default:
            resultTransform = videoAssetTrack.preferredTransform // default landscape orientation nothing need to do there
        }

        return resultTransform
    }
}

这看起来还可以，但是如果视频旋转度不等于90 180，-90或-180度怎么办。

谢谢您的回答。