text: We leverage two types of masks: short-range masks, 
  where we take the union of 8 randomly sampled target 
  blocks covering 15% of each frame, and long-range masks, 
  where we take the union of 2 randomly sampled target 
  blocks covering 70% of each frame. In both cases, the 
  aspect ratio for all sampled blocks is randomly chosen in 
  the range (0.75, 1.5). Given that both short-range and 
  long-range masks are produced by sampling many blocks 
  and taking their union, the result is an average masking 
  ratio of 
  90%. We refer to our masking strategy as 
  multi-block, and compare it to other possible masking 
  strategies in Section 4. 
  
  3.4 Pretraining Data and Evaluation Setup 
  
  ∼ 