Source code for espnet2.asr.decoder.transducer_decoder

"""(RNN-)Transducer decoder definition."""

from typing import Any, Dict, List, Optional, Tuple, Union

import torch
from typeguard import check_argument_types

from espnet2.asr.decoder.abs_decoder import AbsDecoder
from espnet2.asr.transducer.beam_search_transducer import ExtendedHypothesis, Hypothesis

[docs]class TransducerDecoder(AbsDecoder): """(RNN-)Transducer decoder module. Args: vocab_size: Output dimension. layers_type: (RNN-)Decoder layers type. num_layers: Number of decoder layers. hidden_size: Number of decoder units per layer. dropout: Dropout rate for decoder layers. dropout_embed: Dropout rate for embedding layer. embed_pad: Embed/Blank symbol ID. """ def __init__( self, vocab_size: int, rnn_type: str = "lstm", num_layers: int = 1, hidden_size: int = 320, dropout: float = 0.0, dropout_embed: float = 0.0, embed_pad: int = 0, ): assert check_argument_types() if rnn_type not in {"lstm", "gru"}: raise ValueError(f"Not supported: rnn_type={rnn_type}") super().__init__() self.embed = torch.nn.Embedding(vocab_size, hidden_size, padding_idx=embed_pad) self.dropout_embed = torch.nn.Dropout(p=dropout_embed) dec_net = torch.nn.LSTM if rnn_type == "lstm" else torch.nn.GRU self.decoder = torch.nn.ModuleList( [ dec_net(hidden_size, hidden_size, 1, batch_first=True) for _ in range(num_layers) ] ) self.dropout_dec = torch.nn.ModuleList( [torch.nn.Dropout(p=dropout) for _ in range(num_layers)] ) self.dlayers = num_layers self.dunits = hidden_size self.dtype = rnn_type self.odim = vocab_size self.ignore_id = -1 self.blank_id = embed_pad self.device = next(self.parameters()).device
[docs] def set_device(self, device: torch.device): """Set GPU device to use. Args: device: Device ID. """ self.device = device
[docs] def init_state( self, batch_size: int ) -> Tuple[torch.Tensor, Optional[torch.tensor]]: """Initialize decoder states. Args: batch_size: Batch size. Returns: : Initial decoder hidden states. ((N, B, D_dec), (N, B, D_dec)) """ h_n = torch.zeros( self.dlayers, batch_size, self.dunits, device=self.device, ) if self.dtype == "lstm": c_n = torch.zeros( self.dlayers, batch_size, self.dunits, device=self.device, ) return (h_n, c_n) return (h_n, None)
[docs] def rnn_forward( self, sequence: torch.Tensor, state: Tuple[torch.Tensor, Optional[torch.Tensor]], ) -> Tuple[torch.Tensor, Tuple[torch.Tensor, Optional[torch.Tensor]]]: """Encode source label sequences. Args: sequence: RNN input sequences. (B, D_emb) state: Decoder hidden states. ((N, B, D_dec), (N, B, D_dec)) Returns: sequence: RNN output sequences. (B, D_dec) (h_next, c_next): Decoder hidden states. (N, B, D_dec), (N, B, D_dec)) """ h_prev, c_prev = state h_next, c_next = self.init_state(sequence.size(0)) for layer in range(self.dlayers): if self.dtype == "lstm": ( sequence, ( h_next[layer : layer + 1], c_next[layer : layer + 1], ), ) = self.decoder[layer]( sequence, hx=(h_prev[layer : layer + 1], c_prev[layer : layer + 1]) ) else: sequence, h_next[layer : layer + 1] = self.decoder[layer]( sequence, hx=h_prev[layer : layer + 1] ) sequence = self.dropout_dec[layer](sequence) return sequence, (h_next, c_next)
[docs] def forward(self, labels: torch.Tensor) -> torch.Tensor: """Encode source label sequences. Args: labels: Label ID sequences. (B, L) Returns: dec_out: Decoder output sequences. (B, T, U, D_dec) """ init_state = self.init_state(labels.size(0)) dec_embed = self.dropout_embed(self.embed(labels)) dec_out, _ = self.rnn_forward(dec_embed, init_state) return dec_out
[docs] def score( self, hyp: Hypothesis, cache: Dict[str, Any] ) -> Tuple[torch.Tensor, Tuple[torch.Tensor, Optional[torch.Tensor]], torch.Tensor]: """One-step forward hypothesis. Args: hyp: Hypothesis. cache: Pairs of (dec_out, state) for each label sequence. (key) Returns: dec_out: Decoder output sequence. (1, D_dec) new_state: Decoder hidden states. ((N, 1, D_dec), (N, 1, D_dec)) label: Label ID for LM. (1,) """ label = torch.full((1, 1), hyp.yseq[-1], dtype=torch.long, device=self.device) str_labels = "_".join(list(map(str, hyp.yseq))) if str_labels in cache: dec_out, dec_state = cache[str_labels] else: dec_emb = self.embed(label) dec_out, dec_state = self.rnn_forward(dec_emb, hyp.dec_state) cache[str_labels] = (dec_out, dec_state) return dec_out[0][0], dec_state, label[0]
[docs] def batch_score( self, hyps: Union[List[Hypothesis], List[ExtendedHypothesis]], dec_states: Tuple[torch.Tensor, Optional[torch.Tensor]], cache: Dict[str, Any], use_lm: bool, ) -> Tuple[torch.Tensor, Tuple[torch.Tensor, torch.Tensor], torch.Tensor]: """One-step forward hypotheses. Args: hyps: Hypotheses. states: Decoder hidden states. ((N, B, D_dec), (N, B, D_dec)) cache: Pairs of (dec_out, dec_states) for each label sequences. (keys) use_lm: Whether to compute label ID sequences for LM. Returns: dec_out: Decoder output sequences. (B, D_dec) dec_states: Decoder hidden states. ((N, B, D_dec), (N, B, D_dec)) lm_labels: Label ID sequences for LM. (B,) """ final_batch = len(hyps) process = [] done = [None] * final_batch for i, hyp in enumerate(hyps): str_labels = "_".join(list(map(str, hyp.yseq))) if str_labels in cache: done[i] = cache[str_labels] else: process.append((str_labels, hyp.yseq[-1], hyp.dec_state)) if process: labels = torch.LongTensor([[p[1]] for p in process], device=self.device) p_dec_states = self.create_batch_states( self.init_state(labels.size(0)), [p[2] for p in process] ) dec_emb = self.embed(labels) dec_out, new_states = self.rnn_forward(dec_emb, p_dec_states) j = 0 for i in range(final_batch): if done[i] is None: state = self.select_state(new_states, j) done[i] = (dec_out[j], state) cache[process[j][0]] = (dec_out[j], state) j += 1 dec_out =[d[0] for d in done], dim=0) dec_states = self.create_batch_states(dec_states, [d[1] for d in done]) if use_lm: lm_labels = torch.LongTensor( [h.yseq[-1] for h in hyps], device=self.device ).view(final_batch, 1) return dec_out, dec_states, lm_labels return dec_out, dec_states, None
[docs] def select_state( self, states: Tuple[torch.Tensor, Optional[torch.Tensor]], idx: int ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]: """Get specified ID state from decoder hidden states. Args: states: Decoder hidden states. ((N, B, D_dec), (N, B, D_dec)) idx: State ID to extract. Returns: : Decoder hidden state for given ID. ((N, 1, D_dec), (N, 1, D_dec)) """ return ( states[0][:, idx : idx + 1, :], states[1][:, idx : idx + 1, :] if self.dtype == "lstm" else None, )
[docs] def create_batch_states( self, states: Tuple[torch.Tensor, Optional[torch.Tensor]], new_states: List[Tuple[torch.Tensor, Optional[torch.Tensor]]], check_list: Optional[List] = None, ) -> List[Tuple[torch.Tensor, Optional[torch.Tensor]]]: """Create decoder hidden states. Args: states: Decoder hidden states. ((N, B, D_dec), (N, B, D_dec)) new_states: Decoder hidden states. [N x ((1, D_dec), (1, D_dec))] Returns: states: Decoder hidden states. ((N, B, D_dec), (N, B, D_dec)) """ return ([s[0] for s in new_states], dim=1),[s[1] for s in new_states], dim=1) if self.dtype == "lstm" else None, )