code: def test_video_only_frame_video_dataset(self):
      total_duration = 2.0
      with mock_json_annotations() as (
          annotation_json,
          labels,
          duration,
      ):
          clip_sampler = make_clip_sampler("random", total_duration)
          dataset = json_dataset.video_only_dataset(
              data_path=annotation_json,
              clip_sampler=clip_sampler,
              decode_audio=False,
          )
  
          self.assertEqual(dataset.num_videos, 2)
          self.assertEqual(len(list(iter(dataset))), 2)
  
file_path: pytorchvideo/tests/test_data_json_dataset.py
imports: import contextlib
  import json
  import tempfile
  import unittest
  from pytorchvideo.data import json_dataset
  from pytorchvideo.data.clip_sampling import make_clip_sampler
  from pytorchvideo.data.labeled_video_dataset import LabeledVideoDataset
  from utils import temp_frame_video_dataset
label_desc: Use image node_id 4 for calling the TestJsonDatasets obj's underlying member method code with example usage: obj.test_video_only_frame_video_dataset() without return types