Music Seperator (Demucs)

Separate vocals and instrument stems from audio files with Demucs CLI. Use when the user asks for vocal extraction, accompaniment generation, stem splitting, batch separation, output format conversion (wav/flac/mp3), or Demucs performance/memory tuning on CPU/GPU. Also trigger when the user mentions demucs or demucas.

Demucs

Use demucs to split music into stems (default: vocals, drums, bass, other).

Quick start

• Help: demucs --help
• Basic split: demucs "input.mp3"
• Output dir: demucs "input.mp3" -o "D:\\output"
• Vocals only pair: demucs "input.mp3" --two-stems vocals

Prerequisites

• Demucs available: demucs --help or absolute path like D:\demucs-agent-tool\venv\Scripts\demucs.exe --help.
• FFmpeg available: ffmpeg -version must succeed.
• Note: ffmpeg-python is only a Python wrapper and does not install ffmpeg.exe.

Common options

• Model: -n htdemucs (default) or other installed model names.
• Device: -d cuda or -d cpu.
• Chunking: --segment 8 --overlap 0.25 to reduce VRAM/RAM pressure.
• No chunking: --no-split for short audio with enough memory.
• Equivariant shifts: --shifts 1..10 (higher quality, slower).
• Parallel jobs: -j 2 (or more on strong CPUs).

Output format

• Default output is WAV.
• FLAC: demucs "input.mp3" --flac
• MP3: demucs "input.mp3" --mp3 --mp3-bitrate 320 --mp3-preset 2
• Safer clipping behavior: --clip-mode rescale (default) or --clip-mode clamp.

Naming and folder layout

• Default output path pattern: separated/<model>/<track>/<stem>.<ext>.
• Customize names: --filename "{track}/{stem}.{ext}".
• Variables supported: {track}, {trackext}, {stem}, {ext}.

Batch usage

• Multiple files in one call: demucs "a.mp3" "b.wav" "c.flac" -o "D:\\separated".
• Prefer absolute paths for automation scripts and scheduled jobs.

Windows notes

• In venv, executable is usually venv\\Scripts\\demucs.exe.
• Use quoted paths when spaces exist: demucs "D:\\My Music\\song.mp3".
• For external programs, prefer absolute executable path instead of shell activation.
• If non-ASCII paths cause tool/runtime issues, copy input to a temporary ASCII path and run Demucs there.

Troubleshooting

• demucs not found: run python -m demucs --help or call venv\\Scripts\\demucs.exe directly.
• FFmpeg is not installed / ffprobe not found: install FFmpeg and add it to PATH, then verify with ffmpeg -version.
• Out of memory: lower --segment (for example 6 or 4), set -d cpu, or process fewer tracks at once.
• Slow speed on CPU: reduce --shifts, keep chunking enabled, and tune -j.
• Install/network failures: use a stable mirror and longer timeout when running pip.