How to crop video into square iOS with AVAssetWriter

I'm using AVAssetWriter to record a video and I want to be able to crop the video into a square with a offset from the top. Here is my code - ``` 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]; ``` Whenever I uncomment the AVVideoScalingModeKey, the my assetWriter gives me an error about not being able to apply the videoCompressionSettings. I tried using How do make a reduced size video using AVAssetWriter? but it still didn't work for me.