CoreImage坐标系

I have CVPixelBufferRef从一个AVAsset。我正在尝试申请CIFilter到它。我用这些行：

CVPixelBufferRef pixelBuffer = ...
CVPixelBufferRef newPixelBuffer = // empty pixel buffer to fill
CIContex *context = // CIContext created from EAGLContext
CGAffineTransform preferredTransform = // AVAsset track preferred transform
CIImage *phase1 = [CIImage imageWithCVPixelBuffer:pixelBuffer];
CIImage *phase2 = [phase1 imageByApplyingTransform:preferredTransform];
CIImage *phase3 = [self applyFiltersToImage:phase2];

[context render:phase3 toCVPixelBuffer:newPixelBuffer bounds:phase3.extent colorSpace:CGColorSpaceCreateDeviceRGB()];

不幸的是，我得到的结果方向不正确。例如，在肖像模式下拍摄的视频是上下颠倒的。我想问题出在从AVAsset to CoreImage坐标系（在 XCode 中显示预览phase2也呈现出错误的结果）。如何修复它？

我通过这样做解决了这个问题，它应该将所有内容正确定向到坐标空间

var preferredTransform = inst.preferredTransform
preferredTransform.b *= -1
preferredTransform.c *= -1

var outputImage = CIImage(cvPixelBuffer: videoFrameBuffer)
                    .applying(preferredTransform)
outputImage = outputImage.applying(CGAffineTransform(translationX: -outputImage.extent.origin.x, y: -outputImage.extent.origin.y))