将景观视频裁剪为肖像视频

Question

我想裁剪景观视频的异常值，使其具有肖像视频的尺寸比例。

我在这篇文章中读到了关于裁剪的文章：How do I use AVFoundation to crop a video

但我不确定如何设置转换--而且这个答案已经有四年多的历史了，所以我不确定它如何适用于目前可用的更大屏幕尺寸。Tnx！

Answer 1

这似乎起到了关键作用：

AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

AVMutableVideoComposition* videoComposition = [AVMutableVideoComposition videoComposition];
float width = 1080.0/1920.0 * size.height;
videoComposition.renderSize = CGSizeMake(width, size.height);
videoComposition.frameDuration = CMTimeMake(1, 30);

AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30) );

AVMutableVideoCompositionLayerInstruction* transformer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];
CGAffineTransform translate = CGAffineTransformMakeTranslation((width - size.width)/2, 0);
translate = CGAffineTransformScale(translate, 1, 1);

[transformer setTransform:translate atTime:kCMTimeZero];
instruction.layerInstructions = [NSArray arrayWithObject:transformer];
videoComposition.instructions = [NSArray arrayWithObject: instruction];

encoder.videoComposition = videoComposition;