合并AVAsets-缩放以填充

Question

我正在尝试缩放，居中并填充分辨率为1920x1080的标准16：9视频。这些问题似乎不是编码问题，但更多的是我无法解决的数学问题，尤其是对于旋转的视频。

在缩放视频时，我需要做什么以使视频居中，但通常会在视频上留下黑框。我知道这只是和 CGAffineTransformMakeTranslation

一起玩的一种情况

-(CGAffineTransform)exportTransform:(AVAsset *)asset {
AVAssetTrack *track = [asset tracksWithMediaType:AVMediaTypeVideo].firstObject;
UIImageOrientation orientation = UIImageOrientationUp;
BOOL portrait = false;

CGAffineTransform firstTransform = track.preferredTransform;

if(firstTransform.a == 0 && firstTransform.b == 1.0 && firstTransform.c == -1.0 && firstTransform.d == 0) {
    orientation= UIImageOrientationRight;
    portrait = true;
}

if(firstTransform.a == 0 && firstTransform.b == -1.0 && firstTransform.c == 1.0 && firstTransform.d == 0) {
    orientation =  UIImageOrientationLeft;
    portrait = true;

}

if(firstTransform.a == 1.0 && firstTransform.b == 0 && firstTransform.c == 0 && firstTransform.d == 1.0) {
    orientation =  UIImageOrientationUp;

}

if(firstTransform.a == -1.0 && firstTransform.b == 0 && firstTransform.c == 0 && firstTransform.d == -1.0) {
    orientation = UIImageOrientationDown;

}

CGFloat FirstAssetScaleToFitRatio = self.videoresize.height / track.naturalSize.height;
if (portrait) {
    FirstAssetScaleToFitRatio = self.videoresize.width / track.naturalSize.height;
    CGAffineTransform FirstAssetScaleFactor = CGAffineTransformMakeScale(FirstAssetScaleToFitRatio,FirstAssetScaleToFitRatio);
    return CGAffineTransformConcat(track.preferredTransform, FirstAssetScaleFactor);

}
else {
    CGAffineTransform FirstAssetScaleFactor = CGAffineTransformMakeScale(FirstAssetScaleToFitRatio,FirstAssetScaleToFitRatio);
    return CGAffineTransformConcat(CGAffineTransformConcat(track.preferredTransform, FirstAssetScaleFactor),CGAffineTransformMakeTranslation(0.0, -0.0));

}

}