Iphone 如何使用AVAssetWriter将视频裁剪到方形iOS中

我正在使用AVAssetWriter录制视频，我希望能够将视频裁剪成一个从顶部偏移的正方形。这是我的密码-

NSDictionary *videoCleanApertureSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                            @320, AVVideoCleanApertureWidthKey,
                                            @320, AVVideoCleanApertureHeightKey,
                                            @10, AVVideoCleanApertureHorizontalOffsetKey,
                                            @10, AVVideoCleanApertureVerticalOffsetKey,
                                            nil];


NSDictionary *videoAspectRatioSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                          @3, AVVideoPixelAspectRatioHorizontalSpacingKey,
                                          @3,AVVideoPixelAspectRatioVerticalSpacingKey,
                                          nil];



NSDictionary *codecSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               [NSNumber numberWithInteger:bitsPerSecond], AVVideoAverageBitRateKey,
                               @1,AVVideoMaxKeyFrameIntervalKey,
                               videoCleanApertureSettings, AVVideoCleanApertureKey,
                               //AVVideoScalingModeFit,AVVideoScalingModeKey,
                               videoAspectRatioSettings, AVVideoPixelAspectRatioKey,
                               nil];

NSDictionary *videoCompressionSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               codecSettings,AVVideoCompressionPropertiesKey,
                               @320, AVVideoWidthKey,
                               @320, AVVideoHeightKey,
                               nil];

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每当我取消对AVVideoScalingModeKey的注释时，my assetWriter都会提示我无法应用VideoCompression设置的错误。我尝试了使用，但它仍然不适用于我。

我将

AVVideoScalingModeFit，AVVideoScalingModeKey

添加到我的

视频压缩设置中以使其工作。
我尝试了，但我得到了“AvassetWriteInput当前不支持AVVideoScalingModeFit”。有什么新的解决方案可以解决这个问题吗？avassetwriter比avassetexportsession快吗？