Tokenizer directory for a Whisper checkpoint: the model dir itself when
it ships tokenizer.json, else the matching openai/whisper-* HF snapshot
(multilingual v3 vocab → large-v3-turbo; v2 → large-v2; english-only →
base.en). Returns null when nothing is on disk.
Tokenizer directory for a Whisper checkpoint: the model dir itself when it ships tokenizer.json, else the matching openai/whisper-* HF snapshot (multilingual v3 vocab → large-v3-turbo; v2 → large-v2; english-only → base.en). Returns null when nothing is on disk.