Music-only short: Timeline silence, a soundtrack and no duck_db

To make a short with music and no voiceover on Sume, declare the length with audio.mode: "silence" in a Timeline 1.0 render, put the track in soundtrack, and leave duck_db out. Ducking lowers the music under speech, so the docs say it needs a real spine and refuse it on a silent one with duck_requires_audio_spine.

The rules are in the Timeline 1.0 docs (read 2026-10-06). The track itself can come from Music 1.0.

What does silence mode accept?

In silence mode the output length is audio.duration_seconds with no spine file. Do not send url, parts, gain_db or source_in with it. Those combinations return silent_audio_takes_no_url, _parts, _gain or _source_in.

What goes in the soundtrack?

soundtrack is an optional bed with url, gain_db, loop, fade_out_seconds up to 10, and duck_db from 0 to 20. The URL has to be a file on this workspace's media.sume.com. A Music job returns an audio artifact there. Set loop when the track is shorter than the video, and set a fade_out_seconds that is not longer than the output (soundtrack_fade_exceeds_output).

• Ask for the length in the music prompt, since Music 1.0 has no duration field and rejects duration and duration_seconds.
• Music is a fixed $0.125 per accepted generation, and a Timeline render is $0.10 per output minute.
• Check the final file by ear before you post it.

When do I need a spine?

Once there is speech under the music, use that audio as the spine and add duck_db so the bed sits lower while someone talks.