This script converts VIA (VGG Image Annotator) JSON files to .txt files required for YOLOv3.
python via_to_yolo.py --images=path_to_images_folder --json=json_file_path --dest=txt files destination folder --attribute=attribute_name_in_via --labels="{\"label0\":0, \"label1\":1, \"label2\":2}"
This will automatically create txt files in the destination folder needed to train a YOLOv3 model.