Files
VoiceStudio/docs/engines/whisperx.md
T
Palash Debnath 3cae853440 feat(catalogue): one page, one axis — setup summary over per-family engines and weights
The Model Catalogue put the same decision on two axes: an Engines pane with
TTS/ASR/LLM tabs and a Models pane with TTS/ASR/Dictation/Diarisation
sections, dictation shown in both, plus storage stats, the HF token and the
voice-preview toggle parked on the model list. Settings → Voice still carried
Engines and Models entries that only pointed back here.

Now the page reads top-down: a SetupSummary (speech, transcription,
dictation, language model — engine, device, one status word, Change), the
engine list for one family, and that family's downloadable weights under it
(TTS under TTS; offline ASR, streaming dictation and diarisation under ASR;
nothing for LLM, whose engines bring their own). One storage line points at
Settings → Storage.

- ModelStoreTab takes a `family` and scopes sections and the recommendation
  preset to it (scopeReco); stats strip, HF-token toolbar and previews
  panel removed from it.
- Settings: Engines/Models categories and CataloguePointer removed; models
  directory → Storage, HF mirror → Network (both restart-flagged), voice
  previews → Storage. "Manage models" in disk usage opens the catalogue.
- Store: openCatalogue takes a family (pane key tolerated, ignored);
  pendingCatalogueTab gone.
- Engine matrix title is now the locale's plain "Engines".
- i18n: catalogue.* summary keys in all 21 locales; pane/pointer keys dropped.
- Docs: "Model Catalogue → Engines" is "Model Catalogue"; "→ Models" is
  "→ Downloaded weights".
2026-09-10 06:46:09 -07:00

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VoiceStudio — WhisperX Engine

WhisperX is the default ASR engine on CUDA and plain-CPU hosts: faster-whisper (CTranslate2) transcription plus a wav2vec2 forced-alignment pass that snaps word boundaries to ±1030 ms (Whisper's own timestamps are ±100300 ms). That word timing is what dubbing lip-sync depends on, which is why auto-detect prefers it wherever CTranslate2 can use the GPU.

Selecting it

  • Model Catalogue, ASR tab → Use on the WhisperX row, or
  • pin it with OMNIVOICE_ASR_BACKEND=whisperx (the env var always wins over the Settings pick; with neither set, auto-detect chooses per-hardware).

Best at

  • Dubbing — the forced alignment is the accuracy tier lip-sync needs.
  • Batch transcription with word-level subtitles.
  • Multi-speaker work: it pairs with pyannote speaker diarization — see diarization.

Platform support

Host What happens
NVIDIA CUDA GPU, float16 (degrades automatically, see below)
CPU (any OS) int8 — works, but slow for large-v3
Apple Silicon CPU only — CTranslate2 has no Metal build, so auto-detect prefers mlx-whisper there (#1127)
AMD ROCm CPU only — CTranslate2 has no HIP build, so auto-detect prefers pytorch-whisper there (#1529)

Model selection

  • ASR_MODEL_WHISPERX — default large-v3. Accepts the usual size aliases (tinylarge-v3, distil-large-v3) or a full HF repo id. Weights download on first load — see downloading-models.
  • OMNIVOICE_ALIGN_DEVICE — force the wav2vec2 aligner's device. Aligners exist for ~20 major languages; other languages keep Whisper's native word timestamps instead of failing.

VRAM preflight and degradation

Loading fp16 large-v3 onto a nearly-full 8 GB card dies as a native CUDA abort — no Python exception, the whole backend goes down (#723). So before every load the engine checks free VRAM against per-compute-type budgets (float16 5.0 GB, int8_float16 3.5 GB, int8 3.0 GB, scaled down for smaller models) and degrades the compute type — or falls to CPU int8 — instead of starting a load that would kill the process. Disable with OMNIVOICE_ASR_VRAM_PREFLIGHT=0.

Two more fallback chains run at load time:

  • GPUs without efficient fp16 (older Maxwell/Pascal, GTX 16xx) raise a compute-type error — the engine retries int8_float16, then int8 (#551).
  • A genuine CUDA OOM retries on CPU int8, so dubbing still completes (slower, same model and accuracy).

Quirks

  • cuDNN 8 required on CUDA. CTranslate2 links cuDNN 8; if it's missing the process fast-fails with no traceback, so the engine is reported unavailable up front and selection falls through to pytorch-whisper, which uses torch's own cuDNN 9 (#1371).
  • On some hardened Linux kernels CTranslate2's native library is rejected with "cannot enable executable stack" — reported as unavailable, not a crash (#692).
  • A partially-installed environment (interrupted sync, antivirus quarantine) can break WhisperX's deep import chain (whisperx → pyannote → lightning_fabric). The engine is then reported unavailable with a repair hint — reinstall, or uv sync --reinstall on a source checkout (#1185).
  • Audio is decoded through VoiceStudio's validated ffmpeg, not a bare ffmpeg PATH lookup (#479).
  • Transcribes are time-bounded: each dub chunk by OMNIVOICE_TRANSCRIBE_CHUNK_TIMEOUT_S (default 120 s), whole files by OMNIVOICE_ASR_TRANSCRIBE_TIMEOUT_S (default 300 s). Raise them for very long files on slow hardware.

Speed comparisons across engines live in performance.