---
license: cc-by-nc-4.0
language:
- multilingual
library_name: coreml
tags:
- forced-alignment
- mms
- wav2vec2
- ctc
- coreml
- lyrics
- ios
pipeline_tag: automatic-speech-recognition
---

# MMS-FA Multilingual Forced Aligner (CoreML)

On-device CTC **forced aligner** for word-level lyric timestamps, multilingual
(1000+ languages via romanization). Alignment half of a WhisperX-style pipeline:
a transcript is aligned to audio by Viterbi-decoding CTC emissions.

Converted from `torchaudio.pipelines.MMS_FA` (Meta MMS `ctc_alignment_mling_uroman`).

> ⚠️ **LICENSE: CC-BY-NC-4.0 (non-commercial).** Inherited from Meta's MMS
> release. Hosting/attribution is fine; **shipping in a commercial app requires
> resolving the non-commercial restriction first.** For commercial production
> use the Apache-2.0 `wav2vec2-base960h-aligner-coreml` (English) instead, or
> obtain a commercial MMS license / a differently-licensed multilingual model.

## I/O contract

| | |
|---|---|
| input  | `waveform` float32 `[1, 960000]` — a fixed **60 s** window @ 16 kHz mono |
| output | `emissions` float32 `[1, 2999, 28]` — log-probs; **20 ms / frame** (stride 320) |
| dict   | `mms_fa_dict.json` = `{label: index}`, blank `-`=0, then lowercase romanized a–z + apostrophe (no word-separator) |

Text must be **romanized** (uroman) before tokenization for non-Latin scripts.
Long audio: overlapping 60 s windows (hop 50 s), center-crop, single CTC Viterbi
over concatenated emissions. A synthetic star (garbage) token wraps the
transcript to absorb instrumental intros/outros — align on a **separated vocal
stem** for heavily-produced tracks. Precision FLOAT16; target iOS 17.