# Model licensing notes

Records the license basis for ML checkpoints StemDeck downloads at runtime.
Not exhaustive -- only entries where the decision wasn't a simple upstream
license file are documented here.

## Demucs (htdemucs_6s)

MIT, published by the `demucs` PyPI package (Meta/Facebook Research). No
audit needed -- an unambiguous upstream license.

## UVR-MDX-NET Karaoke 2 (on-demand lead/backing vocal split, #275)

- **File**: `UVR_MDXNET_KARA_2.onnx`
- **Distributed via**: `audio-separator` (PyPI, MIT,
  `nomadkaraoke/python-audio-separator`), which bundles/downloads models
  trained as part of the Ultimate Vocal Remover (UVR) project by Anjok07.
- **License**: MIT + attribution, per the `audio-separator` README:
  > "If you choose to integrate this project into some other project using
  > the default model or any other model trained as part of the UVR project,
  > please honor the MIT license by providing credit to UVR and its
  > developers."
- **Credit**: Ultimate Vocal Remover (Anjok07) -- https://github.com/Anjok07/ultimatevocalremovergui

This is the shipped default (`VOCAL_SPLIT_MODEL` in `app/core/config.py`,
overridable via `STEMDECK_KARAOKE_MODEL`).

### Rejected alternative: mel_band_roformer_karaoke (aufr33/viperx)

`audio-separator`'s community-trained roformer checkpoint
(`mel_band_roformer_karaoke_aufr33_viperx_sdr_10.1956.ckpt`) has meaningfully
better reported SDR than the MDX-Net Karaoke 2 model above, and was the
originally preferred choice while scoping this feature. It was rejected after
directly verifying:

- No LICENSE file was ever published for this checkpoint, nor a stated
  license anywhere in its distribution.
- It was originally released through UVR's Boosty supporter-paywall page, not
  as a public open release.
- The public Hugging Face mirror (`jarredou/aufr33-viperx-karaoke-melroformer-model`)
  now returns 401 (gated/removed) -- confirmed directly, not secondhand.

A cleanly-licensed roformer alternative (Kimberley Jensen's
`Mel-Band-Roformer-Vocal-Model`) was also checked and found to have no
LICENSE file despite a claim to the contrary surfacing in a web search.

Since StemDeck is free/non-commercial, the practical risk of using an
unlicensed-but-freely-shared community checkpoint is low -- but a
Boosty-paywall origin is a step past "unlicensed," suggesting the author did
not intend it for free redistribution at all, and its already-dead HF mirror
makes it an unreliable thing to depend on regardless of the licensing
question. `STEMDECK_KARAOKE_MODEL` remains available as an env override for a
deployment that wants to accept that risk itself.