FluidInference/sensevoice-small-coreml

SenseVoiceSmall — CoreML (Apple Neural Engine)

CoreML conversion of FunAudioLLM/SenseVoiceSmall for on-device inference on Apple Silicon, intended for FluidInference/FluidAudio (tracks issues #645 / #646).

SenseVoiceSmall is a non-autoregressive multilingual ASR model (~234M params, SANM encoder + single CTC head) covering 50+ languages, with emotion and audio-event tags. One forward pass yields all output tokens.

Files (3-stage pipeline)

File	Precision	Compute unit	Size	Role
SenseVoicePreprocessor.mlmodelc	FLOAT32	CPU	3 MB	front-end: waveform → 560-d LFR features
SenseVoiceSmall.mlmodelc	FLOAT16	CPU_AND_NE (ANE)	447 MB	default encoder+CTC
SenseVoiceSmall_int8.mlmodelc	INT8 (weights)	CPU_AND_NE (ANE)	225 MB	~half size, accuracy-neutral
SenseVoiceSmall_fp32.mlmodelc	FLOAT32	any	897 MB	encoder fallback (non-ANE)
vocab.json	—	—	—	25055 SentencePiece tokens (array form)

int8 is post-training weight quantization (linear_symmetric), accuracy-neutral vs fp16 on the full canonical sets: LibriSpeech test-clean WER 3.22→3.25% (2,620), AISHELL-1 test CER 3.09→3.09% (7,176) — Δ +0.03 pp / 0.00 pp, 0 NaN on ANE, peak RAM 0.54→0.32 GB. Pick it for ~half the on-disk/memory footprint.

Pipeline: waveform → [Preprocessor, fp32/CPU] → features → [encoder+CTC, fp16/ANE] → logits → host greedy-CTC decode.

⚠️ Compute-unit requirement. The FLOAT16 encoder is numerically correct on the Neural Engine but produces NaN on the CPU/GPU fp16 path. Load it with MLModelConfiguration.computeUnits = .cpuAndNeuralEngine. On hardware without ANE (or under ANE fallback), use SenseVoiceSmall_fp32. The preprocessor must run fp32 (power-spectrum/log exceed fp16 range).

I/O

SenseVoicePreprocessor — in: waveform [1, N] fp32 (16 kHz, scaled ×32768 like kaldi; flexible length). out: features [1, T, 560] fp32.

SenseVoiceSmall (encoder+CTC):

name	shape	dtype	notes
speech	[1, T, 560]	fp32	preprocessor output; T ∈ enumerated buckets [128,256,512,1024,1800] (pad up)
speech_lengths	[1]	int32	valid frame count (before padding)
language	[1]	int32	embed index; 0 = auto
textnorm	[1]	int32	15 = no inverse text-norm (woitn), 14 = withitn

Output: ctc_logits [1, T+4, 25055] — the 4 leading positions are the language/emotion/event/itn query tokens; the rest are the transcript.

Host pre/post-processing

Pre: handled by SenseVoicePreprocessor (kaldi fbank80 → LFR m=7,n=6 → CMVN, matching FunASR WavFrontend to max|Δ|≈2e-5). Pad its output up to the smallest encoder bucket ≥ T.

Post (decode): greedy CTC over ctc_logits → collapse repeats → drop blank (id 0) → SentencePiece detokenize → strip <|...|> tags for the clean transcript. Reference Python in the repo's decode.py.

language/textnorm are embed indices, mapped on the host:

lid_int_dict      = {24884:3, 24885:4, 24888:7, 24892:11, 24896:12, 24992:13}  # <|zh|> etc -> embed idx
textnorm_int_dict = {25016:14, 25017:15}
# language not in dict -> 0 (auto)

Verification & benchmarks

Conversion = PyTorch (FunASR) → torch.jit.trace → coremltools (FLOAT16, EnumeratedShapes, iOS17). Measured on this machine (M-series), FunASR 1.3.9 / coremltools 8.3.

• End-to-end correctness: on the cached zh sample, the CoreML(ANE) → greedy-CTC pipeline reproduces FunASR am.generate exactly: <|zh|><|NEUTRAL|><|Speech|><|woitn|>欢迎大家来体验达摩院推出的语音识别模型

• Parity (torch ↔ CoreML, ANE): CTC argmax token agreement 100% on real audio.

• LibriSpeech test-clean (canonical — matches the official chart): CoreML(ANE) 3.21% WER (torch 3.26%) on n=100 vs the published SenseVoice-Small ~3.1%. Confirms the full pipeline (front-end + CoreML + decode) reproduces the paper. (Full 2620-utt split number: see repo README.)

• FLEURS WER (CoreML ANE vs torch), 100 samples/lang — conversion is accuracy-neutral:

  lang	torch	CoreML (ANE)	Δ	RTFx
  en_us (WER)	9.52%	9.52%	+0.00pp	402
  cmn_hans_cn (CER)	9.60%	9.57%	−0.03pp	372

  FLEURS is a harder/different read-speech set than LibriSpeech/Aishell — its absolute numbers are not comparable to the official benchmark chart; it's used here only for cross-language CoreML↔torch parity.

• RTFx (5.55 s clip, by bucket, ANE): 128→524, 256→274, 512→97, 1024→36, 1800→14.5. (M-series; iPhone ANE not yet measured.)

License & attribution

Weights derive from FunAudioLLM/SenseVoiceSmall; the upstream model license applies. This repo only contains a format conversion (no retraining). See the SenseVoice and FunASR projects.