code: def test_read_partial_video_bframes(self, start, offset):
      # do not use lossless encoding, to test the presence of B-frames
      options = {"bframes": "16", "keyint": "10", "min-keyint": "4"}
      with temp_video(100, 300, 300, 5, options=options) as (
          f_name,
          data,
      ):
          pts, _ = io.read_video_timestamps(f_name)
  
          lv, _, _ = io.read_video(
              f_name, pts[start], pts[start + offset - 1]
          )
          s_data = data[start : (start + offset)]
          assert len(lv) == offset
          assert_equal(s_data, lv, rtol=0.0, atol=self.TOLERANCE)
  
          lv, _, _ = io.read_video(f_name, pts[4] + 1, pts[7])
          # TODO fix this
          if get_video_backend() == "pyav":
              assert len(lv) == 4
              assert_equal(data[4:8], lv, rtol=0.0, atol=self.TOLERANCE)
          else:
              assert len(lv) == 3
              assert_equal(data[5:8], lv, rtol=0.0, atol=self.TOLERANCE)
  
imports: import contextlib
  import os
  import sys
  import tempfile
  import pytest
  import torch
  import torchvision.io
  from common_utils import assert_equal
  from torchvision import get_video_backend
label_desc: Use image node_id 6 for calling the TestVideo obj's underlying member method code with example usage: obj.test_read_partial_video_bframes(start, offset) without return types