resize video

- (void)fixVideoUrl:(NSURL *)url completion:(void (^)(NSURL *outputUrl))completion  {
    // output file
    NSString* docFolder = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString* outputPath = [docFolder stringByAppendingPathComponent:@"output2.mov"];
    if ([[NSFileManager defaultManager] fileExistsAtPath:outputPath]) {
        [[NSFileManager defaultManager] removeItemAtPath:outputPath error:nil];
    }
    
    // input file
    AVAsset* asset = [AVAsset assetWithURL:url];
    
    AVMutableComposition *composition = [AVMutableComposition composition];
    [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    
    // input clip
    AVAssetTrack *clipVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    
    // make it square
    AVMutableVideoComposition* videoComposition = [AVMutableVideoComposition videoComposition];
    //675x379
    //(clipVideoTrack.naturalSize.height, clipVideoTrack.naturalSize.height);
    CGSize size = CGSizeMake(clipVideoTrack.naturalSize.height, clipVideoTrack.naturalSize.height);
    videoComposition.renderSize = size;
    videoComposition.frameDuration = CMTimeMake(1, 30);
    
    AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(60, 30) );
    
    // rotate to portrait
    AVMutableVideoCompositionLayerInstruction* transformer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:clipVideoTrack];
    CGAffineTransform t1 = CGAffineTransformMakeTranslation(clipVideoTrack.naturalSize.height,  - (clipVideoTrack.naturalSize.width - clipVideoTrack.naturalSize.height)/2 );
    //CGAffineTransform t1 = CGAffineTransformMakeTranslation((clipVideoTrack.naturalSize.width - clipVideoTrack.naturalSize.height) /2,-clipVideoTrack.naturalSize.height );
    CGAffineTransform t2 = CGAffineTransformRotate(t1, M_PI_2);
    
    CGAffineTransform finalTransform = t2;
    [transformer setTransform:finalTransform atTime:kCMTimeZero];
    instruction.layerInstructions = [NSArray arrayWithObject:transformer];
    videoComposition.instructions = [NSArray arrayWithObject: instruction];
    
    // export
    __block NSURL *exportUrl = [NSURL fileURLWithPath:outputPath];
    AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality] ;
    exporter.videoComposition = videoComposition;
    exporter.outputURL = exportUrl;
    exporter.outputFileType = AVFileTypeQuickTimeMovie;
    
    [exporter exportAsynchronouslyWithCompletionHandler:^(void) {
        if (exporter.status == AVAssetExportSessionStatusCompleted && completion) {
            completion(exportUrl);
        }
    }];
}