Intel Mac Support: llvmlite build failure and `--list_format=json` crash

[brunodimarco]

Description

There are two sequential installation and runtime bugs when attempting to use the separation runtime on an Intel Mac (x86_64) due to upstream dependency changes dropping support for this architecture.

1. Installation Failure (llvmlite)
Because PyTorch dropped macOS x86_64 support starting with version 2.3, pip automatically backtracks and attempts to install an older version of audio-separator (e.g. 0.24.1) that doesn't strictly require torch>=2.3. During this process, pip tries to install llvmlite. However, llvmlite stopped releasing precompiled macOS x86_64 wheels starting with version 0.46.0. Without a prebuilt wheel, pip attempts to compile it from source, failing because CMake and LLVM are missing.

Installing audio-separator for CPU only failed: /runtime/bin/python', '/private/var/folders/.../ffi/build.py']' returned non-zero exit status 1.
[end of output]
note: This error originates from a subprocess, and is likely not a problem with pip.
ERROR: Failed building wheel for llvmlite

2. Runtime Crash (--list_format=json)
If the user manages to resolve the dependency conflict (e.g., by constraining llvmlite<0.46.0 as proposed below), pip successfully installs audio-separator==0.24.1. However, rx3-toolkit then crashes immediately when attempting to retrieve the model list because audio-separator 0.24.1 does not support the --list_format=json argument:

Model list unavailable: The model list could not be retrieved: ... audio-separator: error: unrecognized arguments: --list_format=json

Steps to Reproduce

1. Run rx3-toolkit on an Intel Mac (or an Apple Silicon Mac running in Rosetta/x86_64 mode).
2. Attempt to provision/install the separation runtime. The installation fails.
3. Fix the installation manually, then try to open the separation UI -> Crash on --list_format=json.

Proposed Fix

We can resolve both issues gracefully for Intel Mac users with two small changes:

Fix 1: Constrain llvmlite for x86_64 macOS

# tools/rx3_stems/provisioning.py
SUPPORT_PACKAGES = [LIBROSA_PIN, "imageio-ffmpeg"]

if sys.platform == "darwin" and platform.machine() == "x86_64":
    # llvmlite >= 0.46.0 lacks macOS x86_64 wheels. 
    # Force < 0.46.0 to avoid source compilation without CMake/LLVM.
    SUPPORT_PACKAGES.append("llvmlite<0.46.0")

SUPPORT_PACKAGES = tuple(SUPPORT_PACKAGES)

Fix 2: Remove --list_format=json
Since older versions of audio-separator (like 0.24.1) output JSON by default and do not recognize the --list_format argument, we should remove it from the subprocess call to maintain compatibility.

# tools/rx3_stems/separation.py (around line 446)
    result = subprocess.run(
        [str(runtime.separator), "--list_models",
         f"--model_file_dir={runtime.models}", "--log_level=error"],
        capture_output=True, text=True,
        env=runtime.subprocess_environment(),
    )

Impact & Tradeoffs

By forcing Intel Macs to use < 0.46.0 of llvmlite (and consequently audio-separator ~0.24.1), users will miss out on the latest optimizations in the audio-separator CLI. However, this is an acceptable and necessary tradeoff because:

1. Version 0.24.1 still fully supports the high-quality core architectures needed by rx3-toolkit (MDX, Demucs, VR, and MDXC/Roformer).
2. It is currently the only automated way to allow Intel Mac users to use the toolkit without forcing them to manually compile LLVM/CMake toolchains from scratch (which most end-users cannot do).

System Info

• OS: macOS (Intel x86_64)
• Python Version: >= 3.10
• rx3-toolkit Version: 0.5.2

[jacksight]

Hmm… my Intel Mac runs this perfectly fine somehow