Annotations and masks in YouTubeVIS2021 dataset

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Hello! There is some difference between a definition of YouTubeVIS2021 dataset from Codalab (https://competitions.codalab.org/competitions/28988#participate-get_data) and annotation files from its links to download. Where is a block annotation{
"id" : int,
"video_id" : int,
"category_id" : int,
"segmentations" : [RLE or [polygon] or None],
"areas" : [float or None],
"bboxes" : [[x,y,width,height] or None],
"iscrowd" : 0 or 1,
} in these json files?
How will a model be trained on this data without any information about masks, boxes ant etc? Сan you advise something how to train the model with my own classes and masks?