docstr: Produces a sample in inference mode with predicted durations.
docstr_tok: ["Produces","a","sample","in","inference","mode","with","predicted","durations","."]
code: def run_inference(self):
      """Produces a sample in inference mode with predicted durations."""
      if self.last_batch is None:
          return
      tokens, *_ = self.last_batch
  
      (
          _,
          postnet_mel_out,
          _,
          _,
          _,
          _,
          _,
          predict_mel_lens,
          _,
          _,
          _,
          _,
      ) = self.hparams.model(tokens)
      self.hparams.progress_sample_logger.remember(
          infer_output=self.process_mel(
              postnet_mel_out, [len(postnet_mel_out[0])]
          )
      )
      return postnet_mel_out, predict_mel_lens
  
imports: import os
  import sys
  import torch
  import logging
  import torchaudio
  import numpy
  import speechbrain
  from speechbrain.inference.vocoders import HIFIGAN
  from pathlib import Path
  from hyperpyyaml import load_hyperpyyaml
  from speechbrain.utils.data_utils import scalarize
label_desc: Use image node_id 8 for calling the FastSpeech2Brain obj's underlying member method code with example usage: obj.run_inference() and returns: postnet_mel_out,  predict_mel_lens