Ace Step

ACE Step — Pro Pack on RunComfy

Tag-driven music generation, inpainting, and outpainting with StepFun-AI's ACE Step open-weights model. Four CLI-reachable endpoints, $0.0002–0.0003 per second of audio, up to 4 minutes per call.

runcomfy.com · ACE Step base · ACE Step 1.5 · CLI docs

Install this skill

npx skills add agentspace-so/runcomfy-agent-skills --skill ace-step -g

Powered by the RunComfy CLI

Step 1 — install (one of, see the runcomfy-cli skill for details):

npm i -g @runcomfy/cli         # global install
npx -y @runcomfy/cli --version # zero-install

Step 2 — sign in (or set RUNCOMFY_TOKEN env var in CI / containers):

runcomfy login

Step 3 — generate:

runcomfy run acestep-ai/ace-step/text-to-audio \
  --input '{"tags": "..."}' \
  --output-dir ./out

CLI deep dive: `runcomfy-cli` skill.

Pick the right endpoint

Listed newest first.

ACE Step 1.5 (text-to-audio) — acestep-ai/ace-step-1.5/text-to-audio

Latest ACE Step generation. 50+ language vocal support, refined structured-lyric handling, otherwise same shape as base. Slightly higher cost ($0.0003/s vs $0.0002/s). Pick for: multilingual lyrics, hero-quality vocal tracks, vocal songs that need clean section structure. Avoid for: cost-sensitive batches where the base model is good enough.

ACE Step (text-to-audio) — acestep-ai/ace-step/text-to-audio (default — cheap & fast)

Original ACE Step. Tag-driven composition, optional lyrics, 5–240 s stereo. $0.0002/s — ~27× cheaper than ElevenLabs Music. Pick for: high-volume drafts, background music, jingles, game loops, cost-sensitive iteration. Avoid for: maximally polished commercial vocal hooks — try ACE Step 1.5 or ElevenLabs Music for those.

ACE Step (audio-inpaint) — acestep-ai/ace-step/audio-inpaint

Regenerate a time range inside an existing track (not mask-based; uses start_time / end_time in seconds, each anchored to track start or end). Pick for: fix a bad chorus in the middle, swap the bridge, replace a 20 s section without re-rendering the whole song. Avoid for: edits that aren't time-bounded — those don't fit the schema.

ACE Step (audio-outpaint) — acestep-ai/ace-step/audio-outpaint

Extend an existing track bidirectionally — add intro before, outro after, or both. Pick for: lengthening a 30 s draft into a 2 min cut, adding a fade-in, building a longer arrangement around an existing hook. Avoid for: extending a track past 4 min total — chain calls instead.

Route 1: ACE Step text-to-audio (default)

Model: acestep-ai/ace-step/text-to-audio (or acestep-ai/ace-step-1.5/text-to-audio for the 1.5 variant)

Schema (both variants — same shape)

Pricing: ACE Step $0.0002/s · ACE Step 1.5 $0.0003/s. 60 s ≈ $0.012 / $0.018; 240 s ≈ $0.048 / $0.072.

Invoke

Tag-driven instrumental:

runcomfy run acestep-ai/ace-step/text-to-audio \
  --input '{
    "tags": "lo-fi hip-hop, mellow, vinyl crackle, rhodes piano, soft drums, 75 BPM",
    "lyrics": "[inst]",
    "duration": 90
  }' \
  --output-dir ./out

Full vocal song with structure (use 1.5 for multilingual):

runcomfy run acestep-ai/ace-step-1.5/text-to-audio \
  --input '{
    "tags": "indie pop, anthemic, electric guitar, driving drums, female vocal, 120 BPM",
    "lyrics": "[Verse]\nChalk on the palms, laces double-knotted\nMorning on the ridge, the sun is rising\n[Chorus]\nWe rise, we strike, we never fade out\nWe rise, we strike, we sing it loud\n[Bridge]\nSoft piano breakdown\n[Outro]\nFull band, fade",
    "duration": 60
  }' \
  --output-dir ./out

Prompting tips

• Tags do the heavy lifting — be specific: "lo-fi hip-hop, mellow, vinyl crackle, rhodes piano, soft drums, 75 BPM" beats "chill music".
• Include BPM in tags when it matters — ACE respects tempo language.
• Lyrics with section markers: [Verse], [Chorus], [Bridge], [Outro]. Keep meter consistent across lines.
• Instrumental shortcut: "lyrics": "[inst]" or "[instrumental]". Belt-and-suspenders: also say "no vocals" in tags.
• Multilingual vocals: ACE Step 1.5 covers 50+ languages. Write lyrics directly in the target language; tag the language too ("japanese vocal, j-pop").
• Fix the seed for reproducibility ("seed": 42); use -1 to explore variations.
• Cheap draft → polish: ACE Step at 5–10× lower cost is great for iterating tags before committing to a long render.

Route 2: ACE Step audio-inpaint

Model: acestep-ai/ace-step/audio-inpaint Catalog: audio-inpaint

Schema

No mask — region is defined purely by start_time / end_time (each anchorable to track start or end).

Invoke

Replace 20–40 s of a track with a new bridge:

runcomfy run acestep-ai/ace-step/audio-inpaint \
  --input '{
    "audio": "https://your-cdn.example/original-track.mp3",
    "tags": "indie pop, breakdown, piano only, soft, no drums",
    "start_time": 20,
    "end_time": 40,
    "lyrics": "[inst]"
  }' \
  --output-dir ./out

Anchor end relative to track end (rewrite the last 15 s):

runcomfy run acestep-ai/ace-step/audio-inpaint \
  --input '{
    "audio": "https://your-cdn.example/song.mp3",
    "tags": "indie pop, fade, soft, ambient pad",
    "start_time": 15,
    "start_time_relative_to": "end",
    "end_time": 0,
    "end_time_relative_to": "end"
  }' \
  --output-dir ./out

Tips

• Match the surrounding tags — if the original is "indie pop, electric guitar, 120 BPM", the inpaint segment should share enough of the tags to blend, not contrast.
• Inpaint window is up to ~4 min even on a 60-min source — pick a focused range, not the whole track.
• Use `_relative_to: "end"` to target the outro/last seconds without computing exact timestamps.

Route 3: ACE Step audio-outpaint

Model: acestep-ai/ace-step/audio-outpaint