src/transformers/models/perceiver/modeling_perceiver.py/PerceiverAudioPreprocessor/num_channels
class PerceiverAudioPreprocessor:    def num_channels(self) -> int:
        # position embedding
        if self.project_pos_dim > 0:
            pos_dim = self.project_pos_dim
        else:
            pos_dim = self.position_embeddings.output_size()
        if self.concat_or_add_pos == "add":
            return pos_dim
        return self.samples_per_patch + pos_dim