code: def forward(self, x, return_all=False):
      if len(x) > 1:
          x, meta, mask = x
      else:
          x, mask = x[0], None
  
      if self.cfg.MASK.MAE_ON:
          return self._mae_forward(
              x, mask_ratio=self.cfg.AUG.MASK_RATIO, mask=mask
          )
      else:
          return self._maskfeat_forward(x, mask, return_all)
  
imports: import math
  from functools import partial
  import torch
  import torch.nn
  import torch.nn.functional
  from torch.nn.init import trunc_normal_
  import slowfast.utils.logging
  import slowfast.utils.misc
  from slowfast.models import head_helper
  from slowfast.models.attention import attention_pool
  from slowfast.models.utils import calc_mvit_feature_geometry
  from slowfast.models.video_model_builder import MViT
  from .None import head_helper, operators, resnet_helper, stem_helper
  from .build import MODEL_REGISTRY
label_desc: Use image node_id 17 for calling the MaskMViT obj's underlying member method code with example usage: obj.forward(x, return_all) and returns: self, self