A 3-minute Short with a ducked music bed: $0.425 on Sume

A 180-second Short with a music bed under your voice costs $0.425 on Sume: Music 1.0 is a fixed $0.125 per generation and a 180-second Timeline 1.0 render is 3 minutes at $0.10 = $0.30 (read 2026-10-08). The reason to generate a track is that YouTube's Audio Library songs may be used for only up to 90 seconds in a 3-minute Short, and some are limited to 60 or 30 seconds.

The YouTube constraint

YouTube says a Short can run up to three minutes in a square or vertical frame. The same page says Shorts Audio Library songs are usable up to 90 seconds in a 3-minute Short, some limited to 60 or 30 seconds, and a Short over one minute with an active Content ID claim is blocked globally and loses monetization. A track you generate and mix yourself is not an Audio Library song, but Content ID risk is yours to judge; Sume does not clear rights for you.

The cost, line by line

Music 1.0 resolves through the Music Router, today to Lyria 3.5, and charges a fixed $0.125 for each accepted generation. It has no duration parameter, so steer length in the prompt, for example 'a 3-minute track'. The Timeline render reserves ceil(180 / 60) = 3 minutes.

Ducking and fades

The soundtrack block takes url, gain_db, loop, fade_out_seconds up to 10, and duck_db from 0 to 20. Ducking needs a real audio spine, so it works with your narration but not with audio.mode: silence. If the generated track comes back shorter than 180 seconds, set loop: true. Check the returned length rather than assuming it, since the docs promise only full-length songs of up to a few minutes.

{
  "audio": { "url": "https://media.sume.com/artifacts/artf_demo/narration.wav", "duration_seconds": 180 },
  "video": [
    { "source_url": "https://media.sume.com/artifacts/artf_demo/part1.mp4", "start": 0, "duration": 90 },
    { "source_url": "https://media.sume.com/artifacts/artf_demo/part2.mp4", "start": 90, "duration": 90,
      "transition": { "type": "dissolve", "duration": 0.5 } }
  ],
  "soundtrack": {
    "url": "https://media.sume.com/artifacts/artf_demo/bed.mp3",
    "gain_db": -6, "loop": true, "duck_db": 12, "fade_out_seconds": 4
  },
  "output": { "width": 1080, "height": 1920 }
}

Prompt tips for the bed

Exclusions go in the positive prompt because negative_prompt is not supported. Write 'instrumental, no vocals, no spoken word, a 3-minute track' rather than a style name alone. Keep the mix at a level that works when ducked, and listen to the first 10 seconds before you spend the render.