You can't ship htdemucs_ft on iOS. You can't ship it on Android. You can't run it in a browser. PyTorch Mobile is a 2 GB install and a permission to break, MLX needs Apple Silicon, and the obvious answer — ONNX — has been "broken on htdemucs" across four open GitHub issues for three years.
I just shipped the first working ONNX export of htdemucs_ft. It runs in onnxruntime, is 1.31× faster than PyTorch on CPU, and is numerically equivalent to the original (max absolute difference: 0.000163 on drums, 0.000008 on vocals). All four specialist sub-models are on Hugging Face: StemSplitio/htdemucs-ft-onnx.
This is the engineering writeup — the 4 blockers that killed every prior attempt and the patches that beat them.
What You'll Learn
Prerequisites
