src/transformers/models/perceiver/modeling_perceiver.py/PerceiverMultimodalPostprocessor/forward
class PerceiverMultimodalPostprocessor:    def forward(
        self, inputs: torch.Tensor, pos: Optional[torch.Tensor] = None, modality_sizes=None
    ) -> Mapping[str, torch.Tensor]:
        if not self.input_is_dict:
            # Slice up modalities by their sizes.
            if modality_sizes is None:
                raise ValueError("Modality sizes should be specified if input is not a dictionary.")
            inputs = restructure(modality_sizes=modality_sizes, inputs=inputs)

        outputs = {
            modality: postprocessor(inputs[modality], pos=pos, modality_sizes=None)
            for modality, postprocessor in self.modalities.items()
        }
        return outputs