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Alkd/
Sortformer-Diarization-CoreML

Name: Sortformer-Diarization-CoreML
Rating: 2.5 (8 reviews)

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Sortformer Diarization (CoreML)

CoreML port of NVIDIA Sortformer for end-to-end streaming speaker diarization on Apple Silicon.

Runs on the Neural Engine via CoreML. No separate embedding extraction or clustering — the model directly predicts per-frame speaker activity for up to 4 speakers.

Model Details

Architecture: Sortformer (Sort Loss + 17-layer FastConformer encoder + 18-layer Transformer)
Base model: nvidia/diar_streaming_sortformer_4spk-v2.1 (117M params)
Task: Speaker diarization (up to 4 speakers)
Input: 128-dim log-mel features, streamed in chunks
Output: Per-frame speaker activity probabilities (sigmoid)
Format: CoreML .mlmodelc (compiled pipeline, 2 sub-models)
Size: ~230 MB

Streaming Configuration

Parameter	Value
Sample rate	16 kHz
Mel bins	128
n_fft	400
Hop length	160
Chunk length	6s
Left context	1 chunk
Right context	7 chunks
Subsampling factor	8
Speaker cache length	188 frames
FIFO length	40 frames
Max speakers	4

Input/Output Shapes

Inputs:

Tensor	Shape	Description
`chunk`	`[1, 112, 128]`	Mel features for current chunk
`chunk_lengths`	`[1]`	Valid frames in chunk
`spkcache`	`[1, 188, 512]`	Speaker cache state
`spkcache_lengths`	`[1]`	Valid entries in speaker cache
`fifo`	`[1, 40, 512]`	FIFO buffer state
`fifo_lengths`	`[1]`	Valid entries in FIFO

Outputs:

Tensor	Shape	Description
`speaker_preds_out`	`[1, 242, 4]`	Speaker activity probabilities
`chunk_pre_encoder_embs_out`	`[1, 14, 512]`	Chunk embeddings for state update
`chunk_pre_encoder_lengths_out`	`[1]`	Valid embedding frames

Usage

Used by speech-swift for speaker diarization:

audio diarize meeting.wav --engine sortformer

swift

let diarizer = try await SortformerDiarizer.fromPretrained()
let result = diarizer.diarize(audio: samples, sampleRate: 16000)
for segment in result.segments {
    print("Speaker \(segment.speakerId): \(segment.startTime)s - \(segment.endTime)s")
}

Pipeline Architecture

The model is a CoreML pipeline with two sub-models:

PreEncoder (model0) — Runs pre_encode on the mel chunk, concatenates with speaker cache and FIFO state
Head (model1) — Full FastConformer encoder + Transformer + sigmoid speaker heads

State management (FIFO rotation, speaker cache compression) is handled in Swift outside the model.

License

CC-BY-4.0

Alkd/Sortformer-Diarization-CoreML