VoiceStudio — MLX Whisper Engine

MLX Whisper runs Whisper on the Apple Silicon GPU via MLX. It exists because CTranslate2 (whisperx / faster-whisper) has no Metal build — on a Mac those engines transcribe on the CPU no matter what GPU is present. Measured on an M2 with whisper-large-v3, one 30 s dub chunk: 90.4 s on WhisperX (CPU) vs 20.5 s on MLX (GPU) — which is why auto-detect picks MLX Whisper on every Apple Silicon machine (#1127).

Selecting it

• Nothing to do on Apple Silicon — auto-detect prefers it there.
• Or explicitly: Model Catalogue → Engines, ASR tab → Use, or OMNIVOICE_ASR_BACKEND=mlx-whisper.

Best at

• Dubbing on a Mac — it layers the same wav2vec2 forced alignment WhisperX uses on top of the GPU transcription, so word timing (±10–30 ms) and therefore lip-sync accuracy are unchanged. Same model, same alignment, ~4x the speed.
• Dictation/capture — the capture path automatically swaps in mlx-community/whisper-large-v3-turbo (~5x faster than large-v3) unless a sherpa dictation model or parakeet-mlx is preferred.

Platform support

Apple Silicon only. A shared platform gate refuses Linux, Windows, and Intel Macs before any package import, so a stray mlx-whisper wheel on the wrong platform never reports itself available (#390). All other platforms use the CUDA/CPU engines instead.

Model selection

• ASR_MODEL — default mlx-community/whisper-large-v3-mlx. Any MLX-format Whisper repo works. Weights download on first load — see downloading-models.
• OMNIVOICE_ALIGN_DEVICE — force the wav2vec2 aligner's device. The aligner runs on MPS when it can and falls back to CPU; languages without a bundled aligner (~20 major languages have one) keep Whisper's native word timestamps.

Quirks

• Audio is decoded through VoiceStudio's validated ffmpeg rather than the bare ffmpeg PATH lookup mlx-whisper would do on its own — a clean from-source install with no system ffmpeg works fine (#479).
• The model is warmed into unified memory in the background, so the first transcribe after startup doesn't pay the load cost.
• In a packaged app, a native MLX library that fails to load is reported as "unavailable" (with fallback to another engine) rather than crashing the engine list.

Speed comparisons across engines live in performance.