Turn an Instagram carousel into a Reel with Sume Timeline

To turn an Instagram carousel into a Reel, import the slide images to Sume, then render them with Timeline 1.0: stills are accepted as static holds, the default output is 1080 by 1920, and audio.mode: "silence" gives you a declared length without a sound file. Meta says reels cannot appear in carousels, so the conversion is a new post, not an edit.

Instagram-side facts come from Meta's IG User Media reference and Content Publishing guide, read 2026-10-02. Timeline behaviour comes from Sume's Timeline 1.0 page.

Why can't I just reuse the carousel?

A carousel container holds up to 10 images, videos, or a mix, and carousel items are cropped to the first image, defaulting to 1:1. Meta also states that Reels cannot appear in carousels and that carousel items are image or video containers, not reels.

The Reel is a different object with different geometry. Square slides on a 9:16 canvas leave empty space unless you choose how to fit them.

How does Timeline handle slides?

Each video[] slot takes a Sume-hosted clip or still. A still is a static hold, and a motion field on a still is accepted and ignored with a motion_ignored warning. The first slot must start at 0, later starts must increase, and each slot lasts at least 0.2 seconds. Transitions of up to 1 second, such as fade or slideup, go on slots after the first.

fit chooses how a non-9:16 still meets the canvas: cover (default) fills and crops, contain letterboxes, stretch distorts, and blur fills the sides with a blurred copy. For square slides, blur keeps every pixel of the slide visible.

curl -X POST https://api.sume.com/v1/timeline-1.0/render \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: carousel-to-reel-001" \
  -d '{
    "audio": {"mode": "silence", "duration_seconds": 12},
    "video": [
      {"source_url": "https://media.sume.com/artifacts/artf_a/s1.jpg", "start": 0, "duration": 4, "fit": "blur"},
      {"source_url": "https://media.sume.com/artifacts/artf_a/s2.jpg", "start": 4, "duration": 4, "fit": "blur", "transition": {"type": "fade", "duration": 0.25}},
      {"source_url": "https://media.sume.com/artifacts/artf_a/s3.jpg", "start": 8, "duration": 4, "fit": "blur", "transition": {"type": "fade", "duration": 0.25}}
    ]
  }'

How long should the Reel be?

Meta's Reel specification lists a minimum of 3 seconds and a maximum of 15 minutes. Ten slides at 3 seconds each is 30 seconds, long enough for a skim and short enough to finish. A timeline can run to 1,800 seconds, so the Instagram limit binds first.

Run the free POST /v1/timeline-1.0/plan first. It returns duration_seconds, segment_count and an estimated cost without creating a job. Rendering is billed at $0.10 per output minute rounded up, so this 12-second example reserves one minute.

What does the Reel not have?

Silent is allowed, but an Instagram Reel with no sound is easy to scroll past. You can lay a soundtrack bed or a voice spine instead of silence. If you use music, check its rights on the Instagram side; see media_audio_type.

Sume does not rank the order of your slides or pick the best ones; you set start and duration per slot. Poll the render through jobs and results and publish the returned video_url as a REELS container.

Which slides work best?

Slides with one idea each convert best: a number, a photo with a short line, a before and after. Dense text slides need longer holds because a Reel advances on its own timer, unlike a carousel that waits for a swipe. Allow roughly one second for every handful of words, and test the pace on a phone.

Keep the slide order as the story order, and set the same fit on every slot so the look stays consistent. If your carousel mixes video and images, both are valid source_url values in the same video[] list.