Crop video to square with a specified side respecting the original video orientation

CropVideo.m

@import MobileCoreServices;
@import AVFoundation;
@import AssetsLibrary;

// ...

- (void)cropVideoAtURL:(NSURL *)videoURL toSquareWithSide:(CGFloat)sideLength completion:(void(^)(NSURL *resultURL, NSError *error))completionHander {
    
    /* asset */

    AVAsset *asset = [AVAsset assetWithURL:videoURL];
    
    AVAssetTrack *assetVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] lastObject];
    
    /* sizes/scales/offsets */
    
    CGSize originalSize = assetVideoTrack.naturalSize;
    
    CGFloat scale;
    
    if (originalSize.width < originalSize.height) {
        scale = sideLength / originalSize.width;
    } else {
        scale = sideLength / originalSize.height;
    }
    
    CGSize scaledSize = CGSizeMake(originalSize.width * scale, originalSize.height * scale);
    
    CGPoint topLeft = CGPointMake(sideLength * .5 - scaledSize.width * .5, sideLength  * .5 - scaledSize.height * .5);
    
    /* Layer instruction */
    
    AVMutableVideoCompositionLayerInstruction *layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:assetVideoTrack];
    
    CGAffineTransform orientationTransform = assetVideoTrack.preferredTransform;

    /* fix the orientation transform */
    
    if (orientationTransform.tx == originalSize.width || orientationTransform.tx == originalSize.height) {
        orientationTransform.tx = sideLength;
    }
    
    if (orientationTransform.ty == originalSize.width || orientationTransform.ty == originalSize.height) {
        orientationTransform.ty = sideLength;
    }
    
    /* -- */

    CGAffineTransform transform = CGAffineTransformConcat(CGAffineTransformConcat(CGAffineTransformMakeScale(scale, scale),  CGAffineTransformMakeTranslation(topLeft.x, topLeft.y)), orientationTransform);

    [layerInstruction setTransform:transform atTime:kCMTimeZero];
    
    /* Instruction */
    
    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];

    instruction.layerInstructions = @[layerInstruction];
    instruction.timeRange = assetVideoTrack.timeRange;
    
    /* Video composition */
    
    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    
    videoComposition.renderSize = CGSizeMake(sideLength, sideLength);
    videoComposition.renderScale = 1.0;
    videoComposition.frameDuration = CMTimeMake(1, 30);
    
    videoComposition.instructions = @[instruction];
    
    /* Export */
    
    AVAssetExportSession *export = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPreset1280x720];
    
    export.videoComposition = videoComposition;
    export.outputURL = [NSURL fileURLWithPath:[[NSTemporaryDirectory() stringByAppendingPathComponent:[NSUUID new].UUIDString] stringByAppendingPathExtension:@"MOV"]];
    export.outputFileType = AVFileTypeQuickTimeMovie;
    export.shouldOptimizeForNetworkUse = YES;
    
    [export exportAsynchronouslyWithCompletionHandler:^{
        dispatch_async(dispatch_get_main_queue(), ^{
            if (export.status == AVAssetExportSessionStatusCompleted) {
                
                completionHander(export.outputURL, nil);
                
            } else {
                
                completionHander(nil, export.error);
                
            }
        });
    }];
    
}