Bg music

Background Music

Generate original, royalty-free instrumental music for reels and demo videos from a text brief - fully offline. A wrapper drives ACE-Step 1.5 (the music model); you (the model) shape the brief into a good prompt, generate a couple of candidates, let the user pick, and optionally mix the winner under a narration.

Pairs with the voice-clone-narration skill: generate the voiceover there, the music here, then mix_voiceover.sh ducks the music under the narration for a finished reel audio track.

flowchart LR
  Brief["brief: genre, mood, bpm, duration"] --> Gen["generate_music.py<br/>ACE-Step 1.5 (MLX), instrumental"]
  Gen --> Mp3["candidate mp3s"]
  Nar["narration.mp3 (optional)"] -.-> Mix["mix_voiceover.sh<br/>ffmpeg sidechain ducking"]
  Mp3 -.-> Mix
  Mix -.-> Reel["reel-audio.mp3"]

Everything lives outside the repo at ~/.bg-music/ (the ACE-Step checkout, model weights, and generated audio).

Prerequisites

• uv (package manager) and git - the model is a uv sync app, not a plain pip install. Setup installs it into an isolated environment.
• ffmpeg on PATH (MP3 encoding + mixing). Stop and ask the user to brew install ffmpeg if missing.
• ~10 GB free disk for the code + model weights (downloaded once from Hugging Face, anonymously - no token). Budget more if you pull larger model variants.
• Apple Silicon Mac for the fast native path (MLX). On CUDA/CPU it falls back to PyTorch (slower on CPU). 16 GB unified memory is enough for the default 2B-turbo + 0.6B-LM tier.
• Internet on first run only (to fetch code + weights). Generation is offline.

Setup

Resolve the skill directory and run setup once (clones ACE-Step 1.5 and syncs its environment - the first run downloads dependencies and can take several minutes):

SKILL_DIR="<the folder this SKILL.md lives in>"   # e.g. .cursor/skills/bg-music
bash "$SKILL_DIR/scripts/setup_env.sh"

Then set the handles used by generation (setup prints these too):

BG_HOME="${BG_MUSIC_HOME:-$HOME/.bg-music}"
PY="$BG_HOME/ACE-Step-1.5/.venv/bin/python"

Workflow

Copy this checklist and track progress:

- [ ] 1. Confirm the brief: genre, mood, tempo (BPM), duration, key instruments
- [ ] 2. Setup: run setup_env.sh (first time only)
- [ ] 3. Write a concrete prompt; generate 2 candidates
- [ ] 4. Play/link the candidates; let the user pick (regenerate if needed)
- [ ] 5. (optional) Mix the winner under a narration mp3 with ducking
- [ ] 6. Deliver the mp3(s)

Step 1: Nail the brief

Music quality depends on a concrete prompt. Pull these from the user (or infer and state your choices):

• Genre/style: lo-fi hip hop, cinematic orchestral, corporate ambient, synthwave, acoustic folk, upbeat pop...
• Mood: calm, uplifting, tense, dreamy, energetic, melancholic.
• Tempo: slow / medium / fast, or an explicit BPM (e.g. 90).
• Duration: seconds (10-600; reels are usually 30-120).
• Key instruments (optional): Rhodes piano, warm pads, soft drums, nylon guitar.

Step 3: Generate

"$PY" "$SKILL_DIR/scripts/generate_music.py" \
  --prompt "warm lo-fi hip hop, mellow Rhodes piano, soft vinyl crackle, laid-back drums, loopable, instrumental" \
  --bpm 80 --duration 60 --count 2 \
  --out "$BG_HOME/out/lofi.mp3"

• Tracks are instrumental by default (no vocals).
• --count 2 produces two variations to choose from (lofi-1.mp3, lofi-2.mp3).
• Writes MP3s and prints their paths + durations. First run downloads model weights; subsequent runs are much faster.

Good prompts are specific and comma-separated. Include genre + mood + 2-3 instruments + a tempo word + "instrumental"/"loopable". Examples:

• "cinematic inspiring orchestral, soft strings, piano, subtle percussion building to a warm swell, instrumental"
• "clean corporate ambient, gentle synth pads, light plucks, optimistic, minimal, instrumental"
• "driving synthwave, analog bass, retro arpeggios, punchy drums, night-drive energy, instrumental"

Step 5: Mix under a narration (optional)

If the user also has a voiceover (e.g. from the voice-clone-narration skill), duck the music under it automatically:

bash "$SKILL_DIR/scripts/mix_voiceover.sh" \
  --voice ~/.voice-clone-narration/out/test-en.mp3 \
  --music "$BG_HOME/out/lofi-1.mp3" \
  --out ~/Desktop/reel-audio.mp3

The music auto-lowers whenever the voice is talking (sidechain compression), then comes back up in the gaps. It is looped to cover the narration and faded in/out. Tune with --music-gain (bed level, default -8 dB), --duck (ducking strength, default 8) and --fade.

Step 6: Deliver

Embed or link the chosen mp3. Generated files stay under ~/.bg-music/out/.

Key options (generate_music.py)

Option	Default	Purpose
--prompt	(required)	Music description: genre, mood, instruments, vibe.
--duration	60	Length in seconds (10-600).
--bpm	auto	Tempo in BPM (30-300); omit to let the model choose.
--count	2	How many variations to generate.
--out	out/music-<ts>.mp3	Output path (or prefix when --count > 1).
--seed	random	Fix for reproducibility.
--keyscale	auto	Musical key, e.g. "A minor".
--vocals	off (instrumental)	Allow vocals (rarely wanted for bg music).
--steps	8	Diffusion steps (turbo default; more = slower, marginally better).
--mp3-quality	2	ffmpeg libmp3lame -q:a (0=best..9=smallest).
--keep-wav	off	Keep the intermediate wav.

Key options (mix_voiceover.sh)

Option	Default	Purpose
--voice	(required)	Narration mp3/wav (stays at full level).
--music	(required)	Background music mp3/wav (gets ducked + looped to cover the voice).
--out	(required)	Output mixed mp3.
--music-gain	-8	Baseline music level in dB (lower = quieter bed).
--duck	8	Ducking strength (compressor ratio); higher = music drops more under speech.
--fade	2	Music fade-in/out seconds.
--mp3-quality	2	ffmpeg libmp3lame -q:a.

Safety

• Disclose AI-generated music where the platform or context calls for it.
• Commercial use: ACE-Step 1.5 is MIT-licensed and trained on licensed / royalty-free / synthetic data, so generated tracks are broadly safe to use. Still, per the model's own disclaimer, avoid prompts that copy a specific artist's or track's identity, and verify originality before commercial release.
• Never upload briefs, prompts, or generated audio to any external service. Everything stays local under ~/.bg-music/.

Anti-patterns

• Vague one-word prompts ("music", "something cool") - you get generic output. Give genre + mood + instruments + tempo.
• Asking for vocals when you only need a bed - keep it instrumental (the default) so it sits under narration cleanly.
• Generating one take and shipping it - generate --count 2 and let the user pick.
• Overlaying music under a voiceover by hand - use mix_voiceover.sh so the music ducks under speech automatically.
• Prompting for "a song that sounds exactly like <artist/track>" - originality and licensing risk.
• Committing anything from ~/.bg-music/ into a repo.

Resources

• Model zoo (why 2B-turbo on 16 GB), the full parameter cheatsheet, prompt patterns by mood, licensing rationale, and troubleshooting: REFERENCE.md
• Generating the narration to mix under the music: the voice-clone-narration skill.
• Verifying the final audio in a video: the review-mp4 skill.