I want to resize the video I took with AVCaptureMovieFileOutput into squares.

// output file
    guardlet docURL=NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains:.UserDomainMask).lastelse{
        print("Failed to find Document directory")
        return
    }
    let outputURL=docURL.URLByAppendingPathComponent("output2.mov")
    if NSFileManager.defaultManager().fileExistsAtPath(outputURL.path!){
        _=try?NSFileManager.defaultManager().removeItemAtURL(outputURL)
    }

    // input file
    let asset = AVAsset (URL: fileURL)

    let composition = AVMutableComposition()
    composition.addMutableTrackWithMediaTypeVideo (AVMediaTypeVideo, preferredTrackID:kCMPPersistentTrackID_Invalid)

    // input clip
    letclipVideoTrack=asset.tracksWithMediaType(AVMediaTypeVideo)[0]

    // make it square
    let videoComposition = AVMutableVideoComposition()
    videoComposition.renderSize=CGSize(width:clipVideoTrack.naturalSize.height, height:clipVideoTrack.naturalSize.height)
    videoComposition.frameDuration=CMTimeMake (1,30)

    let instruction = AVMutableVideoCompositionInstruction()
    instruction.timeRange = CMTimeRangeMake (kCMTimeZero, CMTimeMakeWithSeconds (60,30))

    // rotate to portrait
    let transformer = AVMutableVideoCompositionLayerInstruction (assetTrack: clipVideoTrack)
    lett1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height, -(clipVideoTrack.naturalSize.width-clipVideoTrack.naturalSize.height)/2)
    let t2 = CGAffineTransformRotate(t1, CGFloat(M_PI_2))

    let finalTransform=t2
    transformer.setTransform (finalTransform, atTime:kCMTimeZero)
    instruction.layerInstructions=[transformer]
    videoComposition.instructions=[instruction]

    // export
    guard letter exporter = AVAssetExportSession(asset:asset, presetName:AVAssetExportPresetHighestQuality) else {
        print("Failed to create AVAssetExportSession")
        return
    }
    exporter.videoComposition=videoComposition
    exporter.outputURL = outputURL
    exporter.outputFileType=AVFileTypeQuickTimeMovie

    exporter.exportAsynchronouslyWithCompletionHandler{
        NSLog("Exporting done!")
    }