Now that language model boosted decoding is possible for Wav2Vec2 (https://twitter.com/PatrickPlaten/status/1468999507488788480 11 and patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm · Hugging Face 10
it’s important to know How can one create a Wav2Vec2 + LM repo?.
Let’s explain (hopefully this is simpler in the future):


Install kenlm:
The best guide to build kenlm is this github gist here: kenlm/BUILDING at master · kpu/kenlm · GitHub 14 IMO


Create an ngram model:
This is explained quite well here: GitHub - kpu/kenlm: KenLM: Faster and Smaller Language Model Queries 11
I wrote a short python script that allows to quickly create a ngram from a text corpus of common voice:


#!/usr/bin/env python3
from datasets import load_dataset
import os
import argparse

parser = argparse.ArgumentParser()
parser.add_argument(
    "--language", default="polish", type=str, required=True, help="Language to run comparison on. Choose one of 'polish', 'portuguese', 'spanish' or add more to this script."
)
parser.add_argument(
    "--path_to_ngram", type=str, required=True, help="Path to kenLM ngram"
)
args = parser.parse_args()

ds = load_dataset("multilingual_librispeech", f"{args.language}", split="train")

with open("text.txt", "w") as f:
    f.write(" ".join(ds["text"]))

os.system(f"./kenlm/build/bin/lmplz -o 5 <text.txt > {args.path_to_ngram}")

## VERY IMPORTANT!!!:
# After the language model is created, one should open the file. one should add a `</s>`
# The file should have a structure which looks more or less as follows:

# \data\
# ngram 1=86586
# ngram 2=546387
# ngram 3=796581
# ngram 4=843999
# ngram 5=850874

# \1-grams:
# -5.7532206      <unk>   0
# 0       <s>     -0.06677356
# -3.4645514      drugi   -0.2088903
# ...

# Now it is very important also add a </s> token to the n-gram
# so that it can be correctly loaded. You can simple copy the line:

# 0       <s>     -0.06677356

# and change <s> to </s>. When doing this you should also inclease `ngram` by 1.
# The new ngram should look as follows:

# \data\
# ngram 1=86587
# ngram 2=546387
# ngram 3=796581
# ngram 4=843999
# ngram 5=850874

# \1-grams:
# -5.7532206      <unk>   0
# 0       <s>     -0.06677356
# 0       </s>     -0.06677356
# -3.4645514      drugi   -0.2088903
# ...

# Now the ngram can be correctly used with `pyctcdecode`

See: Wav2Vec2_PyCTCDecode/create_ngram.py at main · patrickvonplaten/Wav2Vec2_PyCTCDecode · GitHub 15
Feel free to copy those lines of code. Multi-Lingual librispeech is already a very clean text corpus. You might want to pre-process other text corpora to not include any punctuation etc…
As an example this step created the Spanish 5-gram here: kensho/5gram-spanish-kenLM · Hugging Face 8

Now we should load the language model in a PyCTCBeamSearchDecoder as this is the format we need. Here one should be very careful to choose exactly the same vocabulary as the Wav2Vec2’s tokenizer vocab.

At first we should pick a fine-tuned Wav2Vec2 model that we would like to add a language model to.
Let’s choose: jonatasgrosman/wav2vec2-large-xlsr-53-spanish · Hugging Face 2
Now we instantiate a BeamSearchDecoder and save it to a folder wav2vec2_with_lm.
E.g. you can run this code:
from transformers import AutoTokenizer
from pyctcdecode import build_ctcdecoder

tokenizer = AutoTokenizer.from_pretrained("jonatasgrosman/wav2vec2-large-xlsr-53-spanish")

vocab_dict = tokenizer.get_vocab()
sorted_dict = {k: v for k, v in sorted(vocab_dict.items(), key=lambda item: item[1])}

decoder = build_ctcdecoder(
    list(sorted_dict.keys()),
    args.path_to_ngram,
)

decoder.save_to_dir("wav2vec2_with_lm")

Now we should have saved the following files in wav2vec2_with_lm:
- language_model
  - attrs.json
  - kenLM.arpa
  - unigrams.txt
- alphabet.json

That’s it! Now all you need to do is to upload this to your Wav2Vec2 model so that the directory structure looks as follows:
  

      huggingface.co
  

  
    

patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm at main 19



  

  
    
    
  

  


Now, all you need to change is your decoding to:
  

      huggingface.co
  

  
    

patrickvonplaten/wav2vec2-large-xlsr-53-spanish-with-lm · Hugging Face 14