Instagram Replace Audio on a published post, or re-render with Sume

If a published Instagram feed post has audio you want to change, use Instagram's own replace-audio flow, because that is the only route that edits the existing post. Instagram's help page for replacing muted audio on a post says that when the music is muted or unavailable you can replace it with a song from Meta's Sound Collection (read 2026-10-03), which means the replacement comes from Instagram's library. Sume cannot upload a track into that flow: nothing in the Sume docs describes it. What Sume can do is render a new file with a different soundtrack, which you then publish as a new post.

The two routes side by side

I could not load Instagram's announcement page, so what happens to likes, comments and reach on replace is not stated here; read Instagram's current help text before you rely on it.

Render the new soundtrack

A Timeline 1.0 render takes an audio spine plus ordered video[] slots. The optional soundtrack is a bed with gain_db, loop, fade_out_seconds up to 10 and duck_db 0-20, which lowers the bed under the spine; ducking needs a real spine, not silence (duck_requires_audio_spine). Generate the bed with the Music Router, which has no duration field, so ask for the length in the prompt.

import json, os, urllib.request

API = "https://api.sume.com/v1"

def post(path, body, key):
    req = urllib.request.Request(
        f"{API}{path}",
        data=json.dumps(body).encode(),
        headers={
            "Authorization": f"Bearer {os.environ['SUME_API_KEY']}",
            "Content-Type": "application/json",
            "Idempotency-Key": key,
        },
        method="POST",
    )
    with urllib.request.urlopen(req) as res:
        return json.load(res)

render = post(
    "/timeline-1.0/render",
    {
        "audio": {"url": os.environ["SUME_VOICE_URL"], "duration_seconds": 20},
        "video": [
            {"source_url": os.environ["SUME_CLIP_URL"], "start": 0, "duration": 20}
        ],
        "soundtrack": {
            "url": os.environ["SUME_MUSIC_URL"],
            "gain_db": -18,
            "loop": True,
            "fade_out_seconds": 2,
            "duck_db": 8,
        },
    },
    "new-soundtrack-001",
)
print(render["request_id"])

Rights and the honest choice

Using Instagram's own flow keeps you inside its music licensing. A file with music baked in is your responsibility, and Instagram can mute or restrict what it detects as unlicensed. If the goal is only a different library track, use the replace flow. If the goal is a different mix (voice ducking, a looped bed, fades) or a brand-owned track, re-render with the original footage and post fresh.

Set the bed under the voice, not over it

The most common reason to change a track is that it fights the voice. duck_db lowers the soundtrack while the spine speaks, from 0 to 20 dB, and gain_db sets the bed's overall level from -60 to 12. A starting point of -18 dB on the bed with 8 dB of ducking keeps music present without masking speech, but listen on a phone speaker before you commit. loop: true repeats a short bed to cover the render, and fade_out_seconds up to 10 closes it cleanly.

Check the plan first. The unbilled POST /v1/timeline-1.0/plan returns the duration and estimated cost without reserving credits, so you can confirm a 20-second render reserves one minute at $0.10 before you submit.

Generating the bed

For a new bed, send a prompt to POST /v1/music-router/generate and omit model to let sume/music-auto choose; today that is Lyria 3.5. The prompt can run up to 5000 characters, and duration and duration_seconds are rejected, so steer length in the words: a 30-second instrumental at a stated tempo. Put exclusions in the positive prompt, such as no vocals. Music is billed at the fixed Music price per generation, not per second.

A short decision list

Run through these before choosing a route.

• Do you only want a different song from Instagram's library on a post that already exists? Use Instagram's replace-audio flow.
• Do you need your own track, a looped bed, or a voice duck? Re-render with the original footage.
• Is the source footage still on hand? If not, a re-render is not possible and the in-app route is the only one.
• Is the post tied to comments or a campaign link you cannot move? Prefer the in-app route and confirm its behavior in Instagram's current help text.
• Are you producing several versions for testing? Render each with its own idempotency key so the retries stay separate.