Ios 自定义AVVideoComposition的AVAsset首选变换

我创建了一个自定义的AVVideoComposition类，并按如下方式使用它：

AVAsset *asset = ...
AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoCompositionWithPropertiesOfAsset:asset];
videoComposition.customVideoCompositorClass = [MyCustomCompositor class];
MyCustomInstruction *instruction = // custom instruction holding CIFilter that is applied to every video frame
videoComposition.instructions = @[instruction];

AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality];
session.outputURL = ...
session.outputFileType = AVFileTypeQuickTimeMovie;
session.videoComposition = videoComposition;

[session exportAsynchronouslyWithCompletionHandler:^{
    ...
}];

导出会话后，使用如下方式：

AVAsset *asset = ...
AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoCompositionWithPropertiesOfAsset:asset];
videoComposition.customVideoCompositorClass = [MyCustomCompositor class];
MyCustomInstruction *instruction = // custom instruction holding CIFilter that is applied to every video frame
videoComposition.instructions = @[instruction];

AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality];
session.outputURL = ...
session.outputFileType = AVFileTypeQuickTimeMovie;
session.videoComposition = videoComposition;

[session exportAsynchronouslyWithCompletionHandler:^{
    ...
}];

如果我使用的是

AVVideoComposition

，则曲目的

preferredTransform

将不起作用。此外，对于自定义

avvideocomposition

指令，我无法使用setTransform:atTime:设置

AVMutableVideoCompositionLayerInstruction

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如何获得方向正确的视频？

请阅读我问题的编辑部分。我见过这个问题，但没用。你解决这个问题了吗，汤姆？我们被困在这些问题上，这是很久以前的事了，所以我不是100%确定。我想我最后是手工修改了转换矩阵。你有没有用过的代码？