YouTube Create drops library music past 15 seconds: bring a bed

Why does my Short lose its Audio Library music on export?

YouTube's help page on adding and editing audio in the Create app says music from the Shorts Audio Library is removed automatically if you export a video longer than 15 seconds. Licensed music is supported for clips up to 60 seconds when you upload directly to YouTube. If your AI-made Short runs 20 or 40 seconds and you exported it from Create with a library track, the track is the part that goes missing.

The way round is to stop depending on the library for that export. Generate a bed yourself, join it to the video in a render you control, and upload the finished file. This post covers that route with Sume tools, and flags the rules YouTube states along the way.

The limits YouTube states

Two help pages mention music limits, and they describe different flows, so keep them apart.

Generate the bed with Music Router

Music Router generates music from a prompt. Omit model or send sume/music-auto and Sume picks the engine; the docs say Lyria 3.5 today. There is no duration field: duration and duration_seconds are rejected, so you steer length in the prompt, for example by asking for a 30-second track. Put exclusions in the positive prompt and add an instrumental clause if the bed sits under speech.

The Music docs list a fixed $0.125 per accepted generation, and the router page says every router model charges the fixed Music price; confirm the live figure in the catalog. Because the length is only steered, ask for a bed a little longer than the Short rather than exactly the same length, and trim it in the render.

Lay the bed under the Short

Timeline 1.0 takes one audio spine plus ordered video slots, and an optional soundtrack. The soundtrack supports gain_db, loop, a fade_out_seconds of up to 10 and duck_db from 0 to 20. Ducking needs a real spine such as a voiceover, not silence mode. The output length is the audio.duration_seconds you declare, so a bed longer than the Short does not stretch it.

The Timeline rate in the docs is $0.10 per ceil(output minute), so any Short up to 60 seconds is one billed minute. For a clip with a 24-second voiceover, a 30-second bed, a ducked mix and a 1.5-second fade, the request looks like this.

{
  "audio": {
    "url": "https://media.sume.com/artifacts/artf_demo/voice.wav",
    "duration_seconds": 24
  },
  "video": [
    {
      "source_url": "https://media.sume.com/artifacts/artf_demo/clip.mp4",
      "start": 0,
      "duration": 24
    }
  ],
  "soundtrack": {
    "url": "https://media.sume.com/artifacts/artf_demo/bed.wav",
    "gain_db": -6,
    "duck_db": 10,
    "fade_out_seconds": 1.5
  },
  "output": { "width": 1080, "height": 1920 }
}

What to check before you rely on it

Sume's docs say nothing about how YouTube's own systems treat a track generated elsewhere, and this post does not make a rights claim. Read the terms for the music engine and YouTube's guidance on matching audio before you upload; the earlier post on Audio Library licensing covers the personal use limits.

Mix levels are easy to get wrong by ear. Render once, listen on a phone speaker, and adjust gain_db or duck_db; the music bed prompt post lists what to put in the prompt so the bed leaves room for a voice.