Swift-裁剪视频帧

Question

我正在尝试裁剪视频而不缩放视频。 此代码将视频裁剪到正确的帧，但也将其缩放到较大的放大比例

func cropVideo(outputFileUrl: URL ) -> (AVMutableVideoComposition)  {

    let videoAsset: AVAsset = AVAsset( url: outputFileUrl )
    let videoComposition = AVMutableVideoComposition()
    let width = ceil(UIScreen.main.bounds.size.width / 16) * 16
    videoComposition.renderSize = CGSize.init(width: width, height: width * (8/6))

    let instruction = AVMutableVideoCompositionInstruction()
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds( videoAsset.duration.seconds, 30 ) )

    if let clipVideoTrack = videoAsset.tracks( withMediaType: AVMediaTypeVideo ).first {

        videoComposition.frameDuration = CMTimeMake(1, Int32(clipVideoTrack.nominalFrameRate))

        let transformer = AVMutableVideoCompositionLayerInstruction( assetTrack: clipVideoTrack )
        let transform1 = CGAffineTransform( translationX: clipVideoTrack.naturalSize.height,
                                            y: -( clipVideoTrack.naturalSize.width - clipVideoTrack.naturalSize.height ) / 2 )

        let transform2 = transform1.rotated(by: CGFloat( Double.pi / 2 ) )

        transformer.setTransform( transform2, at: kCMTimeZero)

        instruction.layerInstructions = [transformer]
    }

    videoComposition.instructions = [instruction]

    return videoComposition
}