[WIP] Refactoring streaming transducer (#78)

* Refactoring streaming transducer

* Refactor code for emformer

* Refactor conv emformer

* Rename decode.py to stream.py

* Refactor offline code

* Refactor offline_asr

* Fix code according to review

* Fix flake8 file and black formating

* Fix offline beam search

* Add keyword arguments

Author: ezerhouni

.flake8

@@ -8,4 +8,5 @@ exclude =
   ./cmake,
   ./triton,
   ./sherpa/python/sherpa/__init__.py,
-  ./sherpa/python/sherpa/decode.py
+  ./sherpa/python/sherpa/decode.py,
+  ./sherpa/python/bin

sherpa/bin/conv_emformer_transducer_stateless2/beam_search.py

@@ -0,0 +1,260 @@
+from typing import List
+
+import k2
+import torch
+from stream import Stream, stack_states, unstack_states
+
+from sherpa import fast_beam_search_one_best, streaming_greedy_search
+
+
+class FastBeamSearch:
+    def __init__(
+        self,
+        vocab_size: int,
+        context_size: int,
+        beam: int,
+        max_states: int,
+        max_contexts: int,
+        device: torch.device,
+    ):
+        """
+        Args:
+          vocab_size:
+            Vocabularize of the BPE
+          context_size:
+            Context size of the RNN-T decoder model.
+          beam:
+            The beam for fast_beam_search decoding.
+          max_states:
+            The max_states for fast_beam_search decoding.
+          max_contexts:
+            The max_contexts for fast_beam_search decoding.
+          device:
+            Device on which the computation will occur
+        """
+        self.rnnt_decoding_config = k2.RnntDecodingConfig(
+            vocab_size=vocab_size,
+            decoder_history_len=context_size,
+            beam=beam,
+            max_states=max_states,
+            max_contexts=max_contexts,
+        )
+        self.decoding_graph = k2.trivial_graph(vocab_size - 1, device)
+        self.device = device
+        self.context_size = context_size
+
+    def init_stream(self, stream: Stream):
+        """
+        Attributes to add to each stream
+        """
+        stream.rnnt_decoding_stream = k2.RnntDecodingStream(self.decoding_graph)
+        stream.hyp = []
+
+    @torch.no_grad()
+    def process(
+        self,
+        server: "StreamingServer",
+        stream_list: List[Stream],
+    ) -> None:
+        """Run the model on the given stream list and do search with fast_beam_search
+           method.
+        Args:
+          server:
+            An instance of `StreamingServer`.
+          stream_list:
+            A list of streams to be processed. It is changed in-place.
+            That is, the attribute `states` and `hyp` are
+            updated in-place.
+        """
+        model = server.model
+        device = model.device
+        # Note: chunk_length is in frames before subsampling
+        chunk_length = server.chunk_length
+        batch_size = len(stream_list)
+        chunk_length_pad = server.chunk_length_pad
+        state_list, feature_list = [], []
+        processed_frames_list, rnnt_decoding_streams_list = [], []
+
+        rnnt_decoding_config = self.rnnt_decoding_config
+        for s in stream_list:
+            rnnt_decoding_streams_list.append(s.rnnt_decoding_stream)
+            state_list.append(s.states)
+            processed_frames_list.append(s.processed_frames)
+            f = s.features[:chunk_length_pad]
+            s.features = s.features[chunk_length:]
+            s.processed_frames += chunk_length
+
+            b = torch.cat(f, dim=0)
+            feature_list.append(b)
+
+        features = torch.stack(feature_list, dim=0).to(device)
+
+        states = stack_states(state_list)
+
+        features_length = torch.full(
+            (batch_size,),
+            fill_value=features.size(1),
+            device=device,
+            dtype=torch.int64,
+        )
+
+        num_processed_frames = torch.tensor(
+            processed_frames_list, device=device
+        )
+
+        (
+            encoder_out,
+            encoder_out_lens,
+            next_states,
+        ) = model.encoder_streaming_forward(
+            features=features,
+            features_length=features_length,
+            num_processed_frames=num_processed_frames,
+            states=states,
+        )
+
+        processed_lens = (num_processed_frames >> 2) + encoder_out_lens
+        next_hyp_list = fast_beam_search_one_best(
+            model=model,
+            encoder_out=encoder_out,
+            processed_lens=processed_lens,
+            rnnt_decoding_config=rnnt_decoding_config,
+            rnnt_decoding_streams_list=rnnt_decoding_streams_list,
+        )
+
+        next_state_list = unstack_states(next_states)
+        for i, s in enumerate(stream_list):
+            s.states = next_state_list[i]
+            s.hyp = next_hyp_list[i]
+
+    def get_texts(self, stream: Stream):
+        """
+        Return text after decoding
+        Args:
+          stream:
+            Stream to be processed.
+        """
+        return self.sp.decode(stream.hyp)
+
+
+class GreedySearch:
+    def __init__(self, model: "RnntConvEmformerModel", device: torch.device):
+        """
+        Args:
+          model:
+            RNN-T model decoder model
+          device:
+            Device on which the computation will occur
+        """
+
+        self.blank_id = model.blank_id
+        self.context_size = model.context_size
+        self.device = device
+
+        decoder_input = torch.tensor(
+            [[self.blank_id] * self.context_size],
+            device=self.device,
+            dtype=torch.int64,
+        )
+        initial_decoder_out = model.decoder_forward(decoder_input)
+        self.initial_decoder_out = model.forward_decoder_proj(
+            initial_decoder_out.squeeze(1)
+        )
+
+    def init_stream(self, stream: Stream):
+        """
+        Attributes to add to each stream
+        """
+        stream.decoder_out = self.initial_decoder_out
+        stream.hyp = [self.blank_id] * self.context_size
+
+    @torch.no_grad()
+    def process(
+        self,
+        server: "StreamingServer",
+        stream_list: List[Stream],
+    ) -> None:
+        """Run the model on the given stream list and do search with greedy_search
+           method.
+        Args:
+          server:
+            An instance of `StreamingServer`.
+          stream_list:
+            A list of streams to be processed. It is changed in-place.
+            That is, the attribute `states` and `hyp` are
+            updated in-place.
+        """
+        model = server.model
+        device = model.device
+        # Note: chunk_length is in frames before subsampling
+        chunk_length = server.chunk_length
+        batch_size = len(stream_list)
+        chunk_length_pad = server.chunk_length_pad
+        state_list, feature_list = [], []
+        decoder_out_list, hyp_list = [], []
+        processed_frames_list = []
+
+        for s in stream_list:
+            decoder_out_list.append(s.decoder_out)
+            hyp_list.append(s.hyp)
+            state_list.append(s.states)
+            processed_frames_list.append(s.processed_frames)
+            f = s.features[:chunk_length_pad]
+            s.features = s.features[chunk_length:]
+            s.processed_frames += chunk_length
+
+            b = torch.cat(f, dim=0)
+            feature_list.append(b)
+
+        features = torch.stack(feature_list, dim=0).to(device)
+        states = stack_states(state_list)
+        decoder_out = torch.cat(decoder_out_list, dim=0)
+
+        features_length = torch.full(
+            (batch_size,),
+            fill_value=features.size(1),
+            device=device,
+            dtype=torch.int64,
+        )
+
+        num_processed_frames = torch.tensor(
+            processed_frames_list, device=device
+        )
+
+        (
+            encoder_out,
+            encoder_out_lens,
+            next_states,
+        ) = model.encoder_streaming_forward(
+            features=features,
+            features_length=features_length,
+            num_processed_frames=num_processed_frames,
+            states=states,
+        )
+
+        # Note: It does not return the next_encoder_out_len since
+        # there are no paddings for streaming ASR. Each stream
+        # has the same input number of frames, i.e., server.chunk_length.
+        next_decoder_out, next_hyp_list = streaming_greedy_search(
+            model=model,
+            encoder_out=encoder_out,
+            decoder_out=decoder_out,
+            hyps=hyp_list,
+        )
+
+        next_decoder_out_list = next_decoder_out.split(1)
+
+        next_state_list = unstack_states(next_states)
+        for i, s in enumerate(stream_list):
+            s.states = next_state_list[i]
+            s.decoder_out = next_decoder_out_list[i]
+            s.hyp = next_hyp_list[i]
+
+    def get_texts(self, stream: Stream):
+        """
+        Return text after decoding
+        Args:
+          stream:
+            Stream to be processed.
+        """
+        return self.sp.decode(stream.hyp[self.context_size :])

sherpa/bin/conv_emformer_transducer_stateless2/decode.py renamed to sherpa/bin/conv_emformer_transducer_stateless2/stream.py

@@ -15,9 +15,8 @@
 # limitations under the License.
 
 import math
-from typing import List, Optional, Tuple
+from typing import List, Tuple
 
-import k2
 import torch
 from kaldifeat import FbankOptions, OnlineFbank, OnlineFeature
 
@@ -154,29 +153,15 @@ class Stream(object):
     def __init__(
         self,
         context_size: int,
-        blank_id: int,
         initial_states: List[List[torch.Tensor]],
-        decoding_method: str = "greedy_search",
-        decoding_graph: Optional[k2.Fsa] = None,
-        decoder_out: Optional[torch.Tensor] = None,
     ) -> None:
         """
         Args:
           context_size:
             Context size of the RNN-T decoder model.
-          blank_id:
-            Blank token ID of the BPE model.
           initial_states:
             The initial states of the Emformer model. Note that the state
             does not contain the batch dimension.
-          decoding_method:
-            The decoding method to use, currently, only greedy_search and
-            fast_beam_search are supported.
-          decoding_graph:
-            The Fsa based decoding graph for fast_beam_search.
-          decoder_out:
-            The initial decoder out corresponding to the decoder input
-            `[blank_id]*context_size`
         """
         self.feature_extractor = _create_streaming_feature_extractor()
         # It contains a list of 2-D tensors representing the feature frames.
@@ -185,26 +170,8 @@ def __init__(
         self.num_fetched_frames = 0
 
         self.states = initial_states
-        self.decoding_graph = decoding_graph
-
-        if decoding_method == "fast_beam_search":
-            assert decoding_graph is not None
-            self.rnnt_decoding_stream = k2.RnntDecodingStream(decoding_graph)
-            self.hyp = []
-        elif decoding_method == "greedy_search":
-            assert decoder_out is not None
-            self.decoder_out = decoder_out
-            self.hyp = [blank_id] * context_size
-        else:
-            # fmt: off
-            raise ValueError(
-                f"Decoding method {decoding_method} is not supported."
-            )
-            # fmt: on
-
         self.processed_frames = 0
         self.context_size = context_size
-        self.hyp = [blank_id] * context_size
         self.log_eps = math.log(1e-10)
 
     def accept_waveform(