#!/usr/bin/env python3
"""Perform CTC segmentation to align utterances within audio files.
This uses the ctc-segmentation Python package.
Install it with pip or see the installing instructions in
https://github.com/lumaku/ctc-segmentation
Authors
* Ludwig Kürzinger 2021
"""
import logging
from pathlib import Path
from types import SimpleNamespace
from typing import Optional
from typing import Union
import numpy as np
import torch
from typing import List
# speechbrain interface
from speechbrain.inference.ASR import EncoderASR, EncoderDecoderASR
# imports for CTC segmentation
try:
from ctc_segmentation import ctc_segmentation
from ctc_segmentation import CtcSegmentationParameters
from ctc_segmentation import determine_utterance_segments
from ctc_segmentation import prepare_text
from ctc_segmentation import prepare_token_list
except ImportError:
print(
"ImportError: "
"Is the ctc_segmentation module installed "
"and in your PYTHONPATH?"
)
raise ImportError("The ctc_segmentation module is missing.")
logger = logging.getLogger(__name__)
[docs]
class CTCSegmentationTask(SimpleNamespace):
"""Task object for CTC segmentation.
This object is automatically generated and acts as
a container for results of a CTCSegmentation object.
When formatted with str(·), this object returns
results in a kaldi-style segments file formatting.
The human-readable output can be configured with
the printing options.
Attributes
----------
text : list
Utterance texts, separated by line. But without the utterance
name at the beginning of the line (as in kaldi-style text).
ground_truth_mat : array
Ground truth matrix (CTC segmentation).
utt_begin_indices : np.ndarray
Utterance separator for the Ground truth matrix.
timings : np.ndarray
Time marks of the corresponding chars.
state_list : list
Estimated alignment of chars/tokens.
segments : list
Calculated segments as: (start, end, confidence score).
config : CtcSegmentationParameters
CTC Segmentation configuration object.
name : str
Name of aligned audio file (Optional). If given, name is
considered when generating the text.
Default: "utt".
utt_ids : list
The list of utterance names (Optional). This list should
have the same length as the number of utterances.
lpz : np.ndarray
CTC posterior log probabilities (Optional).
print_confidence_score : bool
Include the confidence score.
Default: True.
print_utterance_text : bool
Include utterance text.
Default: True.
"""
text = None
ground_truth_mat = None
utt_begin_indices = None
timings = None
char_probs = None
state_list = None
segments = None
config = None
done = False
# Optional
name = "utt"
utt_ids = None
lpz = None
# Printing
print_confidence_score = True
print_utterance_text = True
[docs]
def set(self, **kwargs):
"""Update object attributes."""
self.__dict__.update(kwargs)
[docs]
def __str__(self):
"""Return a kaldi-style ``segments`` file (string)."""
output = ""
num_utts = len(self.segments)
if self.utt_ids is None:
utt_names = [f"{self.name}_{i:04}" for i in range(num_utts)]
else:
# ensure correct mapping of segments to utterance ids
assert num_utts == len(self.utt_ids)
utt_names = self.utt_ids
for i, boundary in enumerate(self.segments):
# utterance name and file name
utt_entry = f"{utt_names[i]} {self.name} "
# segment start and end
utt_entry += f"{boundary[0]:.2f} {boundary[1]:.2f}"
# confidence score
if self.print_confidence_score:
utt_entry += f" {boundary[2]:3.4f}"
# utterance ground truth
if self.print_utterance_text:
utt_entry += f" {self.text[i]}"
output += utt_entry + "\n"
return output
[docs]
class CTCSegmentation:
"""Align text to audio using CTC segmentation.
Usage
-----
Initialize with given ASR model and parameters.
If needed, parameters for CTC segmentation can be set with ``set_config(·)``.
Then call the instance as function to align text within an audio file.
Attributes
---------
asr_model : EncoderDecoderASR
Speechbrain ASR interface. This requires a model that has a
trained CTC layer for inference. It is better to use a model with
single-character tokens to get a better time resolution.
Please note that the inference complexity with Transformer models
usually increases quadratically with audio length.
It is therefore recommended to use RNN-based models, if available.
kaldi_style_text : bool
A kaldi-style text file includes the name of the
utterance at the start of the line. If True, the utterance name
is expected as first word at each line. If False, utterance
names are automatically generated. Set this option according to
your input data. Default: True.
text_converter : str
How CTC segmentation handles text.
"tokenize": Use the ASR model tokenizer to tokenize the text.
"classic": The text is preprocessed as text pieces which takes
token length into account. If the ASR model has longer tokens,
this option may yield better results. Default: "tokenize".
time_stamps : str
Choose the method how the time stamps are
calculated. While "fixed" and "auto" use both the sample rate,
the ratio of samples to one frame is either automatically
determined for each inference or fixed at a certain ratio that
is initially determined by the module, but can be changed via
the parameter ``samples_to_frames_ratio``. Recommended for
longer audio files: "auto".
**ctc_segmentation_args
Parameters for CTC segmentation.
The full list of parameters is found in ``set_config``.
Example
-------
>>> # using example file included in the SpeechBrain repository
>>> from speechbrain.inference.ASR import EncoderDecoderASR
>>> from speechbrain.alignment.ctc_segmentation import CTCSegmentation
>>> # load an ASR model
>>> pre_trained = "speechbrain/asr-transformer-transformerlm-librispeech"
>>> asr_model = EncoderDecoderASR.from_hparams(source=pre_trained) # doctest: +SKIP
>>> aligner = CTCSegmentation(asr_model, kaldi_style_text=False) # doctest: +SKIP
>>> # load data
>>> audio_path = "tests/samples/single-mic/example1.wav"
>>> text = ["THE BIRCH CANOE", "SLID ON THE", "SMOOTH PLANKS"]
>>> segments = aligner(audio_path, text, name="example1") # doctest: +SKIP
On multiprocessing
------------------
To parallelize the computation with multiprocessing, these three steps
can be separated:
(1) ``get_lpz``: obtain the lpz,
(2) ``prepare_segmentation_task``: prepare the task, and
(3) ``get_segments``: perform CTC segmentation.
Note that the function `get_segments` is a staticmethod and therefore
independent of an already initialized CTCSegmentation obj́ect.
References
----------
CTC-Segmentation of Large Corpora for German End-to-end Speech Recognition
2020, Kürzinger, Winkelbauer, Li, Watzel, Rigoll
https://arxiv.org/abs/2007.09127
More parameters are described in https://github.com/lumaku/ctc-segmentation
"""
fs = 16000
kaldi_style_text = True
samples_to_frames_ratio = None
time_stamps = "auto"
choices_time_stamps = ["auto", "fixed"]
text_converter = "tokenize"
choices_text_converter = ["tokenize", "classic"]
warned_about_misconfiguration = False
config = CtcSegmentationParameters()
[docs]
def __init__(
self,
asr_model: Union[EncoderASR, EncoderDecoderASR],
kaldi_style_text: bool = True,
text_converter: str = "tokenize",
time_stamps: str = "auto",
**ctc_segmentation_args,
):
"""Initialize the CTCSegmentation module."""
# Prepare ASR model
if (
isinstance(asr_model, EncoderDecoderASR)
and not (
hasattr(asr_model, "mods")
and hasattr(asr_model.mods, "decoder")
and hasattr(asr_model.mods.decoder, "ctc_weight")
)
) or (
isinstance(asr_model, EncoderASR)
and not (
hasattr(asr_model, "mods")
and hasattr(asr_model.mods, "encoder")
and hasattr(asr_model.mods.encoder, "ctc_lin")
)
):
raise AttributeError("The given asr_model has no CTC module!")
if not hasattr(asr_model, "tokenizer"):
raise AttributeError(
"The given asr_model has no tokenizer in asr_model.tokenizer!"
)
self.asr_model = asr_model
self._encode = self.asr_model.encode_batch
if isinstance(asr_model, EncoderDecoderASR):
# Assumption: log-softmax is already included in ctc_forward_step
self._ctc = self.asr_model.mods.decoder.ctc_forward_step
else:
# Apply log-softmax to encoder output
self._ctc = self.asr_model.hparams.log_softmax
self._tokenizer = self.asr_model.tokenizer
# Apply configuration
self.set_config(
fs=self.asr_model.hparams.sample_rate,
time_stamps=time_stamps,
kaldi_style_text=kaldi_style_text,
text_converter=text_converter,
**ctc_segmentation_args,
)
# determine token or character list
char_list = [
asr_model.tokenizer.id_to_piece(i)
for i in range(asr_model.tokenizer.vocab_size())
]
self.config.char_list = char_list
# Warn about possible misconfigurations
max_char_len = max([len(c) for c in char_list])
if len(char_list) > 500 and max_char_len >= 8:
logger.warning(
f"The dictionary has {len(char_list)} tokens with "
f"a max length of {max_char_len}. This may lead "
f"to low alignment performance and low accuracy."
)
[docs]
def set_config(
self,
time_stamps: Optional[str] = None,
fs: Optional[int] = None,
samples_to_frames_ratio: Optional[float] = None,
set_blank: Optional[int] = None,
replace_spaces_with_blanks: Optional[bool] = None,
kaldi_style_text: Optional[bool] = None,
text_converter: Optional[str] = None,
gratis_blank: Optional[bool] = None,
min_window_size: Optional[int] = None,
max_window_size: Optional[int] = None,
scoring_length: Optional[int] = None,
):
"""Set CTC segmentation parameters.
Parameters for timing
---------------------
time_stamps : str
Select method how CTC index duration is estimated, and
thus how the time stamps are calculated.
fs : int
Sample rate. Usually derived from ASR model; use this parameter
to overwrite the setting.
samples_to_frames_ratio : float
If you want to directly determine the
ratio of samples to CTC frames, set this parameter, and
set ``time_stamps`` to "fixed".
Note: If you want to calculate the time stamps from a model
with fixed subsampling, set this parameter to:
``subsampling_factor * frame_duration / 1000``.
Parameters for text preparation
-------------------------------
set_blank : int
Index of blank in token list. Default: 0.
replace_spaces_with_blanks : bool
Inserts blanks between words, which is
useful for handling long pauses between words. Only used in
``text_converter="classic"`` preprocessing mode. Default: False.
kaldi_style_text : bool
Determines whether the utterance name is expected
as fist word of the utterance. Set at module initialization.
text_converter : str
How CTC segmentation handles text.
Set at module initialization.
Parameters for alignment
------------------------
min_window_size : int
Minimum number of frames considered for a single
utterance. The current default value of 8000 corresponds to
roughly 4 minutes (depending on ASR model) and should be OK in
most cases. If your utterances are further apart, increase
this value, or decrease it for smaller audio files.
max_window_size : int
Maximum window size. It should not be necessary
to change this value.
gratis_blank : bool
If True, the transition cost of blank is set to zero.
Useful for long preambles or if there are large unrelated segments
between utterances. Default: False.
Parameters for calculation of confidence score
----------------------------------------------
scoring_length : int
Block length to calculate confidence score. The
default value of 30 should be OK in most cases.
30 corresponds to roughly 1-2s of audio.
"""
# Parameters for timing
if time_stamps is not None:
if time_stamps not in self.choices_time_stamps:
raise NotImplementedError(
f"Parameter ´time_stamps´ has to be one of "
f"{list(self.choices_time_stamps)}",
)
self.time_stamps = time_stamps
if fs is not None:
self.fs = float(fs)
if samples_to_frames_ratio is not None:
self.samples_to_frames_ratio = float(samples_to_frames_ratio)
# Parameters for text preparation
if set_blank is not None:
self.config.blank = int(set_blank)
if replace_spaces_with_blanks is not None:
self.config.replace_spaces_with_blanks = bool(
replace_spaces_with_blanks
)
if kaldi_style_text is not None:
self.kaldi_style_text = bool(kaldi_style_text)
if text_converter is not None:
if text_converter not in self.choices_text_converter:
raise NotImplementedError(
f"Parameter ´text_converter´ has to be one of "
f"{list(self.choices_text_converter)}",
)
self.text_converter = text_converter
# Parameters for alignment
if min_window_size is not None:
self.config.min_window_size = int(min_window_size)
if max_window_size is not None:
self.config.max_window_size = int(max_window_size)
if gratis_blank is not None:
self.config.blank_transition_cost_zero = bool(gratis_blank)
if (
self.config.blank_transition_cost_zero
and self.config.replace_spaces_with_blanks
and not self.warned_about_misconfiguration
):
logger.error(
"Blanks are inserted between words, and also the transition cost of"
" blank is zero. This configuration may lead to misalignments!"
)
self.warned_about_misconfiguration = True
# Parameter for calculation of confidence score
if scoring_length is not None:
self.config.score_min_mean_over_L = int(scoring_length)
[docs]
def get_timing_config(self, speech_len=None, lpz_len=None):
"""Obtain parameters to determine time stamps."""
timing_cfg = {
"index_duration": self.config.index_duration,
}
# As the parameter ctc_index_duration vetoes the other
if self.time_stamps == "fixed":
# Initialize the value, if not yet available
if self.samples_to_frames_ratio is None:
ratio = self.estimate_samples_to_frames_ratio()
self.samples_to_frames_ratio = ratio
index_duration = self.samples_to_frames_ratio / self.fs
else:
assert self.time_stamps == "auto"
samples_to_frames_ratio = speech_len / lpz_len
index_duration = samples_to_frames_ratio / self.fs
timing_cfg["index_duration"] = index_duration
return timing_cfg
[docs]
def estimate_samples_to_frames_ratio(self, speech_len=215040):
"""Determine the ratio of encoded frames to sample points.
This method helps to determine the time a single encoded frame occupies.
As the sample rate already gave the number of samples, only the ratio
of samples per encoded CTC frame are needed. This function estimates them by
doing one inference, which is only needed once.
Arguments
---------
speech_len : int
Length of randomly generated speech vector for single
inference. Default: 215040.
Returns
-------
int
Estimated ratio.
"""
random_input = torch.rand(speech_len)
lpz = self.get_lpz(random_input)
lpz_len = lpz.shape[0]
# CAVEAT assumption: Frontend does not discard trailing data!
samples_to_frames_ratio = speech_len / lpz_len
return samples_to_frames_ratio
[docs]
@torch.no_grad()
def get_lpz(self, speech: Union[torch.Tensor, np.ndarray]):
"""Obtain CTC posterior log probabilities for given speech data.
Arguments
---------
speech : Union[torch.Tensor, np.ndarray]
Speech audio input.
Returns
-------
np.ndarray
Numpy vector with CTC log posterior probabilities.
"""
if isinstance(speech, np.ndarray):
speech = torch.tensor(speech)
# Batch data: (Nsamples,) -> (1, Nsamples)
speech = speech.unsqueeze(0).to(self.asr_model.device)
wav_lens = torch.tensor([1.0]).to(self.asr_model.device)
enc = self._encode(speech, wav_lens)
# Apply ctc layer to obtain log character probabilities
lpz = self._ctc(enc).detach()
# Shape should be ( <time steps>, <classes> )
lpz = lpz.squeeze(0).cpu().numpy()
return lpz
def _split_text(self, text):
"""Convert text to list and extract utterance IDs."""
utt_ids = None
# Handle multiline strings
if isinstance(text, str):
text = text.splitlines()
# Remove empty lines
text = list(filter(len, text))
# Handle kaldi-style text format
if self.kaldi_style_text:
utt_ids_and_text = [utt.split(" ", 1) for utt in text]
# remove utterances with empty text
utt_ids_and_text = filter(lambda ui: len(ui) == 2, utt_ids_and_text)
utt_ids_and_text = list(utt_ids_and_text)
utt_ids = [utt[0] for utt in utt_ids_and_text]
text = [utt[1] for utt in utt_ids_and_text]
return utt_ids, text
[docs]
def prepare_segmentation_task(self, text, lpz, name=None, speech_len=None):
"""Preprocess text, and gather text and lpz into a task object.
Text is pre-processed and tokenized depending on configuration.
If ``speech_len`` is given, the timing configuration is updated.
Text, lpz, and configuration is collected in a CTCSegmentationTask
object. The resulting object can be serialized and passed in a
multiprocessing computation.
It is recommended that you normalize the text beforehand, e.g.,
change numbers into their spoken equivalent word, remove special
characters, and convert UTF-8 characters to chars corresponding to
your ASR model dictionary.
The text is tokenized based on the ``text_converter`` setting:
The "tokenize" method is more efficient and the easiest for models
based on latin or cyrillic script that only contain the main chars,
["a", "b", ...] or for Japanese or Chinese ASR models with ~3000
short Kanji / Hanzi tokens.
The "classic" method improves the the accuracy of the alignments
for models that contain longer tokens, but with a greater complexity
for computation. The function scans for partial tokens which may
improve time resolution.
For example, the word "▁really" will be broken down into
``['▁', '▁r', '▁re', '▁real', '▁really']``. The alignment will be
based on the most probable activation sequence given by the network.
Arguments
---------
text : list
List or multiline-string with utterance ground truths.
lpz : np.ndarray
Log CTC posterior probabilities obtained from the CTC-network;
numpy array shaped as ( <time steps>, <classes> ).
name : str
Audio file name that will be included in the segments output.
Choose a unique name, or the original audio
file name, to distinguish multiple audio files. Default: None.
speech_len : int
Number of sample points. If given, the timing
configuration is automatically derived from length of fs, length
of speech and length of lpz. If None is given, make sure the
timing parameters are correct, see time_stamps for reference!
Default: None.
Returns
-------
CTCSegmentationTask
Task object that can be passed to
``CTCSegmentation.get_segments()`` in order to obtain alignments.
"""
config = self.config
# Update timing parameters, if needed
if speech_len is not None:
lpz_len = lpz.shape[0]
timing_cfg = self.get_timing_config(speech_len, lpz_len)
config.set(**timing_cfg)
# `text` is needed in the form of a list.
utt_ids, text = self._split_text(text)
# Obtain utterance & label sequence from text
if self.text_converter == "tokenize":
# list of str --tokenize--> list of np.array
token_list = [
np.array(self._tokenizer.encode_as_ids(utt)) for utt in text
]
# filter out any instances of the <unk> token
unk = config.char_list.index("<unk>")
token_list = [utt[utt != unk] for utt in token_list]
ground_truth_mat, utt_begin_indices = prepare_token_list(
config, token_list
)
else:
assert self.text_converter == "classic"
text_pieces = [
"".join(self._tokenizer.encode_as_pieces(utt)) for utt in text
]
# filter out any instances of the <unk> token
text_pieces = [utt.replace("<unk>", "") for utt in text_pieces]
ground_truth_mat, utt_begin_indices = prepare_text(
config, text_pieces
)
task = CTCSegmentationTask(
config=config,
name=name,
text=text,
ground_truth_mat=ground_truth_mat,
utt_begin_indices=utt_begin_indices,
utt_ids=utt_ids,
lpz=lpz,
)
return task
[docs]
@staticmethod
def get_segments(task: CTCSegmentationTask):
"""Obtain segments for given utterance texts and CTC log posteriors.
Arguments
---------
task : CTCSegmentationTask
Task object that contains ground truth and
CTC posterior probabilities.
Returns
-------
dict
Dictionary with alignments. Combine this with the task
object to obtain a human-readable segments representation.
"""
assert type(task) == CTCSegmentationTask
assert task.config is not None
config = task.config
lpz = task.lpz
ground_truth_mat = task.ground_truth_mat
utt_begin_indices = task.utt_begin_indices
text = task.text
# Align using CTC segmentation
timings, char_probs, state_list = ctc_segmentation(
config, lpz, ground_truth_mat
)
# Obtain list of utterances with time intervals and confidence score
segments = determine_utterance_segments(
config, utt_begin_indices, char_probs, timings, text
)
# Store results
result = {
"name": task.name,
"timings": timings,
"char_probs": char_probs,
"state_list": state_list,
"segments": segments,
"done": True,
}
return result
[docs]
def __call__(
self,
speech: Union[torch.Tensor, np.ndarray, str, Path],
text: Union[List[str], str],
name: Optional[str] = None,
) -> CTCSegmentationTask:
"""Align utterances.
Arguments
---------
speech : Union[torch.Tensor, np.ndarray, str, Path]
Audio file that can be given as path or as array.
text : Union[List[str], str]
List or multiline-string with utterance ground truths.
The required formatting depends on the setting ``kaldi_style_text``.
name : str
Name of the file. Utterance names are derived from it.
Returns
-------
CTCSegmentationTask
Task object with segments. Apply str(·) or print(·) on it
to obtain the segments list.
"""
if isinstance(speech, str) or isinstance(speech, Path):
speech = self.asr_model.load_audio(speech)
# Get log CTC posterior probabilities
lpz = self.get_lpz(speech)
# Conflate text & lpz & config as a segmentation task object
task = self.prepare_segmentation_task(text, lpz, name, speech.shape[0])
# Apply CTC segmentation
segments = self.get_segments(task)
task.set(**segments)
return task