[`Whisper`] Add conversion script for the tokenizer (#27338)

* draft

* updates

* full conversion taken from `https://gist.github.com/xenova/a452a6474428de0182b17605a98631ee`



* psuh

* nits

* updates

* more nits

* Add co author
Co-authored-by: Joshua Lochner <admin@xenova.com>

* fixup

* cleanup

* styling

* add proper path

* update

* nits

* don't  push the exit

* clean

* update whisper doc

* don't error out if tiktoken is not here

* make sure we are BC with conversion

* nit

* Update docs/source/en/model_doc/whisper.md
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* merge and update

* update markdwon

* Co-authored-by: Sanchit Gandhi <93869735+sanchit-gandhi@users.noreply.github.com>

---------
Co-authored-by: Joshua Lochner <admin@xenova.com>
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

docs/source/en/model_doc/whisper.md

@@ -34,8 +34,13 @@ The original code can be found [here](https://github.com/openai/whisper).
 - Inference is currently only implemented for short-form i.e. audio is pre-segmented into <=30s segments. Long-form (including timestamps) will be implemented in a future release.
 - One can use [`WhisperProcessor`] to prepare audio for the model, and decode the predicted ID's back into text.
 
-This model was contributed by [Arthur Zucker](https://huggingface.co/ArthurZ). The Tensorflow version of this model was contributed by [amyeroberts](https://huggingface.co/amyeroberts).
-The original code can be found [here](https://github.com/openai/whisper).
+- To convert the tokenizer, we recommend using the following:
+
+```bash
+python src/transformers/models/whisper/convert_openai_to_hf.py --checkpoint_path "" --pytorch_dump_folder_path "Arthur/whisper-3" --convert_tokenizer True --whisper_version 3 --multilingual True
+```
+Here the `whisper_version` will set the number of languages to `100` to account for `cantonese` which was added in `whisper-large-v3`.
+
 
 ## Inference
 

src/transformers/models/whisper/convert_openai_to_hf.py

@@ -17,7 +17,9 @@
 import argparse
 import hashlib
 import io
+import json
 import os
+import tempfile
 import urllib
 import warnings
 
@@ -25,7 +27,9 @@ import torch
 from torch import nn
 from tqdm import tqdm
 
-from transformers import WhisperConfig, WhisperForConditionalGeneration
+from transformers import WhisperConfig, WhisperForConditionalGeneration, WhisperTokenizer
+from transformers.models.whisper.tokenization_whisper import LANGUAGES, bytes_to_unicode
+from transformers.utils.import_utils import _is_package_available
 
 
 _MODELS = {
@@ -41,6 +45,11 @@ _MODELS = {
     "large-v2": "https://openaipublic.azureedge.net/main/whisper/models/81f7c96c852ee8fc832187b0132e569d6c3065a3252ed18e56effd0b6a73e524/large-v2.pt",
 }
 
+_TOKENIZERS = {
+    "multilingual": "https://raw.githubusercontent.com/openai/whisper/main/whisper/assets/multilingual.tiktoken",
+    "english": "https://raw.githubusercontent.com/openai/whisper/main/whisper/assets/gpt2.tiktoken",
+}
+
 
 def remove_ignore_keys_(state_dict):
     ignore_keys = ["layers", "blocks"]
@@ -178,11 +187,119 @@ def convert_openai_whisper_to_tfms(checkpoint_path, pytorch_dump_folder_path):
     model.save_pretrained(pytorch_dump_folder_path)
 
 
+# Adapted from https://github.com/openai/tiktoken/issues/60#issuecomment-1499977960
+def _bpe(mergeable_ranks, token: bytes, max_rank=None) -> list[bytes]:
+    parts = [bytes([b]) for b in token]
+    while True:
+        min_idx = None
+        min_rank = None
+        for i, pair in enumerate(zip(parts[:-1], parts[1:])):
+            rank = mergeable_ranks.get(pair[0] + pair[1])
+            if rank is not None and (min_rank is None or rank < min_rank):
+                min_idx = i
+                min_rank = rank
+        if min_rank is None or (max_rank is not None and min_rank >= max_rank):
+            break
+        assert min_idx is not None
+        parts = parts[:min_idx] + [parts[min_idx] + parts[min_idx + 1]] + parts[min_idx + 2 :]
+    return parts
+
+
+def convert_tiktoken_bpe_to_hf(tiktoken_url: str):
+    bpe_ranks = load_tiktoken_bpe(tiktoken_url)
+    byte_encoder = bytes_to_unicode()
+
+    def token_bytes_to_string(b):
+        return "".join([byte_encoder[ord(char)] for char in b.decode("latin-1")])
+
+    merges = []
+    vocab = {}
+    for token, rank in bpe_ranks.items():
+        vocab[token_bytes_to_string(token)] = rank
+        if len(token) == 1:
+            continue
+        merged = tuple(_bpe(bpe_ranks, token, max_rank=rank))
+        if len(merged) == 2:  # account for empty token
+            merges.append(" ".join(map(token_bytes_to_string, merged)))
+    return vocab, merges
+
+
+def convert_tiktoken_to_hf(
+    pytorch_dump_folder_path: str, multilingual: bool = True, num_languages: int = 100, time_precision=0.02
+) -> WhisperTokenizer:
+    # requires whisper, unless we use the path to the tiktoken file
+    tiktoken_tokenizer_path = _TOKENIZERS["multilingual" if multilingual else "english"]
+    start_of_transcript = ["<|endoftext|>", "<|startoftranscript|>"]
+    control_tokens = [
+        "<|translate|>",
+        "<|transcribe|>",
+        "<|startoflm|>",
+        "<|startofprev|>",
+        "<|nocaptions|>",
+        "<|notimestamps|>",
+    ]
+    # these are special tokens, not normalized
+    language_tokens = [f"<|{k}|>" for k in list(LANGUAGES)[:num_languages]]
+    # These are not special but normalized
+    timestamp_tokens = [("<|%.2f|>" % (i * time_precision)) for i in range(1500 + 1)]
+
+    vocab, merges = convert_tiktoken_bpe_to_hf(tiktoken_tokenizer_path)
+
+    with tempfile.TemporaryDirectory() as tmpdirname:
+        vocab_file = f"{tmpdirname}/vocab.json"
+        merge_file = f"{tmpdirname}/merges.txt"
+        with open(vocab_file, "w", encoding="utf-8") as f:
+            f.write(json.dumps(vocab, indent=2, sort_keys=True, ensure_ascii=False) + "\n")
+
+        with open(merge_file, "w", encoding="utf-8") as writer:
+            writer.write("#version: 0.2\n")
+            for bpe_tokens in merges:
+                writer.write(bpe_tokens + "\n")
+
+        hf_tokenizer = WhisperTokenizer(vocab_file, merge_file)
+
+    hf_tokenizer.add_tokens(start_of_transcript + language_tokens + control_tokens, special_tokens=True)
+    hf_tokenizer.add_tokens(timestamp_tokens, special_tokens=False)
+    hf_tokenizer.save_pretrained(pytorch_dump_folder_path)
+
+
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
     # # Required parameters
     parser.add_argument("--checkpoint_path", type=str, help="Patht to the downloaded checkpoints")
     parser.add_argument("--pytorch_dump_folder_path", default=None, type=str, help="Path to the output PyTorch model.")
+    parser.add_argument(
+        "--convert_tokenizer",
+        type=bool,
+        default=False,
+        help="Whether or not the tokenizer should be converted along with the model.",
+    )
+    parser.add_argument(
+        "--whisper_version",
+        type=int,
+        default=2,
+        help="Version of the whisper release",
+    )
+    parser.add_argument(
+        "--multilingual",
+        type=bool,
+        default="store_true",
+        help="Whether or not the model is multilingual or english only",
+    )
     args = parser.parse_args()
 
+    if args.convert_tokenizer:
+        try:
+            if not _is_package_available("tiktoken"):
+                raise """`tiktoken` is not installed, use `pip install tiktoken` to convert the tokenizer"""
+        except Exception:
+            pass
+        else:
+            from tiktoken.load import load_tiktoken_bpe
+
+            NUM_LANGUAGES_PER_RELEASE = {1: 99, 2: 99, 3: 100}
+            convert_tiktoken_to_hf(
+                args.pytorch_dump_folder_path, args.multilingual, NUM_LANGUAGES_PER_RELEASE[args.whisper_version]
+            )
+
     convert_openai_whisper_to_tfms(args.checkpoint_path, args.pytorch_dump_folder_path)

src/transformers/models/whisper/tokenization_whisper.py

@@ -191,6 +191,7 @@ LANGUAGES = {
     "ba": "bashkir",
     "jw": "javanese",
     "su": "sundanese",
+    "yue": "cantonese",
 }
 
 # language code lookup by name, with a few language aliases
@@ -207,6 +208,7 @@ TO_LANGUAGE_CODE = {
     "moldovan": "ro",
     "sinhalese": "si",
     "castilian": "es",
+    "mandarin": "zh",
 }
 
 TASK_IDS = ["translate", "transcribe"]
@@ -1206,7 +1208,7 @@ def _combine_tokens_into_words(
     if language is None:
         language = "english"
 
-    if language in {"chinese", "japanese", "thai", "lao", "myanmar"}:
+    if language in {"chinese", "japanese", "thai", "lao", "myanmar", "cantonese"}:
         # These languages don't typically use spaces.
         words, word_tokens, token_indices = _split_tokens_on_unicode(tokenizer, tokens)
     else: