Dream Track prompt limit: 50 characters, and a longer brief on Sume

Dream Track limits the prompt to 50 characters in the YouTube app. In the YouTube Create app the limit is 85 characters. YouTube's help page states both numbers, and says prompts are also subject to several safety features. Everything beyond that is the model's guess, so a detailed brief needs a different tool.

Sume's Music Router accepts prompts of 1 to 5000 characters. This post compares the two, lists who can use Dream Track, and shows a request with a longer brief.

What are Dream Track's limits?

Dream Track is a set of experimental tools for generating music for Shorts and for image posts that appear in the Shorts feed. You describe a song, pick an artist in the YouTube app, and preview the song and lyrics. The soundtrack carries a text label saying it was created with Dream Track.

Why does a 50-character prompt limit matter?

Fifty characters is a phrase, such as a genre and a mood. It leaves no room for tempo, instruments or a section plan. If you want a track that changes at a set second, or one that has no vocals, you need room to say so.

Sume's Music Router docs show a prompt that includes a tempo, a key, instruments, a moment at 0:10, a length and an instruction for no vocals. They also say to put exclusions in the positive prompt and to steer length in the prompt itself, such as a 2-minute track, because duration and duration_seconds are rejected.

What does a longer brief look like on Sume?

Send the prompt to POST /v1/music-router/generate. With model omitted it routes to sume/music-auto, which is Lyria 3.5 today. Music 1.0 is priced at a fixed $0.125 per accepted generation, and the Music Router doc says every router model charges the fixed Music price per audio generation, so the price does not change with prompt length.

curl -X POST https://api.sume.com/v1/music-router/generate \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: dream-track-alt-001" \
  -d '{
    "model": "sume/music-auto",
    "prompt": "Upbeat synth-pop, 118 BPM, A minor. Plucky arpeggio intro, drums enter at 0:04, bright chorus lift at 0:12. A 30-second track. Instrumental, no vocals."
  }'

How do I get the file?

Poll GET /v1/jobs/{id}/status, then read GET /v1/jobs/{id}/result. The audio is in result.artifacts[] where type is audio, and result.lyrics carries a lyrics or section map when present. The file is a durable media.sume.com artifact, which you can use as the audio spine or as a soundtrack bed in Timeline 1.0, with duck_db to lower it under a voice.

That is the main practical difference from Dream Track: the soundtrack made inside YouTube cannot be downloaded, while a Sume track is a file you hold.

Which should I use?

Use Dream Track when you want to stay in the app and are happy with a short phrase prompt. Use the Music Router when you need a longer brief, a length, or a track to mix under your own clips. Either way, read YouTube's monetization pages for Shorts music before you rely on a track, and check whether your upload needs an AI label. This post does not cover those rules.