Audio Ducking

Sonilo Audio Ducking

Automatically duck a music bed under a voice track: Sonilo lowers the music wherever the voice is speaking and lifts it back in the gaps, then returns the mixed result. The voice input may be a video — its audio track is used as the voice, and the ducked mix is muxed back into a new video.

Setup: See the setup-api-key skill.

⚠️ Cost: makes an API call that may incur charges. Only call when explicitly requested.

Transport: MCP or CLI

Pick one at the start of the session and stay on it. Do not mix the two inside a single job, and do not announce the choice.

1. Sonilo MCP tools visible in this session (audio_ducking and friends) — use them. This is the preferred path: it needs no shell, and it is the only one that survives a very long generation. If a call fails to authenticate — rather than failing on its inputs — this transport is not usable in this session: go to 2 instead of retrying it.
2. No usable Sonilo MCP tools, but sonilo account exits 0 — use the CLI commands below. Same API, same account, same credential file. Probe with sonilo account, not sonilo whoami: whoami exits 0 even when signed out, so it cannot tell the two states apart.
3. Neither — stop and run the setup-api-key skill. Do not call api.sonilo.com with curl to work around it; both transports handle uploads, polling and retries that a bare request does not.

Quick Start

MCP tool call (recommended)

audio_ducking(
    voice_path="~/Desktop/interview.mp4",
    music_path="~/Desktop/background-track.wav"
)

Python (pip install "sonilo>=0.13")

from sonilo import Sonilo

client = Sonilo()  # reads SONILO_API_KEY

result = client.audio_ducking.generate(
    voice="interview.mp4",  # audio or video; also voice_url=
    music="background-track.wav",  # audio only; also music_url=
)
result.save("ducked.mp4" if result.output_type == "video" else "ducked.wav")

JavaScript / TypeScript (npm install sonilo@>=0.14)

import { SoniloClient, download } from "sonilo";
import { writeFile } from "node:fs/promises";

const client = new SoniloClient(); // reads SONILO_API_KEY

const result = await client.audioDucking.generate({
  voice: "./interview.mp4", // audio or video; also voiceUrl
  musicUrl: "https://example.com/background-track.wav", // audio only; also music
});
await writeFile(
  result.output_type === "video" ? "ducked.mp4" : "ducked.wav",
  await download(result.output_url!),
);

CLI (npm install -g sonilo-cli or pip install sonilo-cli)

sonilo audio-ducking --voice interview.mp4 --music-url https://example.com/background-track.wav

Always async under the hood — the CLI submits and polls for you. Exactly one of --voice/--voice-url and one of --music/--music-url. The default output name follows what comes back (output.wav, or output.mp4 when the voice input was a video); --output overrides it. A local --music file must have an audio extension — the CLI rejects a video there up front, for the same reason the MCP tool does.

cURL (raw REST API, no MCP host)

curl -X POST "https://api.sonilo.com/v1/audio-ducking" \
  -H "Authorization: Bearer $SONILO_API_KEY" \
  -F "voice_file=@interview.mp4" \
  -F "music_file=@background-track.wav"
# -> {"task_id": "..."}  poll GET /v1/tasks/{task_id}

A local file uses the voice_file/music_file multipart fields; a remote source uses voice_url/music_url form fields instead (mix and match freely between the two inputs).

Tool

Parameters

Each input is capped at 360 seconds (6 minutes) and by the account's upload-size limit (typically 300 MB).

Workflow Tips

• This tool takes two already-existing tracks — it does not generate music or SFX itself. If you need to generate the music bed first, use the text-to-music or video-to-music skill (text_to_music/video_to_music), then feed the result in here as music_path.
• The voice input can be a video. If the user hands you a talking-head clip or an interview and a separate music file, pass the video straight through as voice_path — Sonilo extracts its audio track, ducks the music under it, and re-muxes the ducked mix back into a new video automatically.
• Prefer video-to-sound or video_to_music(ducking=true) when the music itself is also being generated for that same video — those tools duck internally as part of generation, so you don't need a separate ducking call. Reach for audio_ducking specifically when the music track is fixed/external and you just need the mix.

Recovering a Timed-Out Call

This tool submits an async task on the backend. If the call times out, the error carries a task_id — the job keeps running (already charged). Call get_sfx_task(task_id) later (get_generation_task(task_id) on the hosted server); see task-recovery.

Output Files

A single file: a .wav if the voice input was audio, or a .mp4 (ducked mix re-muxed in) if the voice input was a video. Named after the voice input (e.g. interview.mp4 → interview-ducked.mp4), falling back to ducked-<first 8 chars of the task id>.

Error Handling

Common errors: 401 invalid key, 402 insufficient balance / trial exhausted, 413 file too large, 422 invalid parameters, 429 rate limit. See the account skill.