Descript music at a set length vs Sume music length in the prompt

Descript's September 17 changelog entry says you can generate music and sound effects at specified lengths. Sume's Music Router works differently: duration and duration_seconds are rejected, and you steer length in the prompt itself, for example "a 2-minute track" or section markers like [0:00-0:30] Intro. Treat the result as approximately that long, then check the file.

The two approaches

The Descript line is from its changelog; the Sume lines are from the Music Router docs.

A prompt that asks for length

Put the length and the section plan in one prompt, up to 5,000 characters. job.request.routed_model tells you which engine ran, and the audio lands as an artifact on the job result.

import os, requests

r = requests.post(
    "https://api.sume.com/v1/music-router/generate",
    headers={"Authorization": f"Bearer {os.environ['SUME_API_KEY']}",
             "Idempotency-Key": "music-len-001"},
    json={"model": "sume/music-auto",
          "prompt": "A 45-second corporate intro. [0:00-0:15] soft piano, "
                    "[0:15-0:45] build with strings. Instrumental."},
)
print(r.status_code, r.json())

If the length is wrong

Because length is only guided, a generation can come back shorter or longer than asked. Trim with timeline audio split rather than re-rolling, and re-roll only if the structure missed.

Worked example

Here is how to turn a length requirement into a prompt.

• Need 45 seconds: say "a 45-second track" and add [0:00-0:15] and [0:15-0:45] section lines.
• Need exactly 30 seconds for a spot: ask for 35 and trim with timeline audio split.
• Need a loop: ask for a steady section and join copies with timeline audio concat (1 to 20 parts).

Checklist before you commit

Because the router rejects duration outright, a payload that includes it fails fast with an error, which is useful for catching copy-pasted examples from other APIs.

• Check the real length of every generated file.
• Keep the prompt with the artifact.
• Budget $0.125 per accepted generation, including retries you decide to keep.