Threads ads specs: video ratios, the 4:5 crop, and captions

Threads ads can be image, video, or carousel ads. Meta's developer docs say Threads supports video from 1.91:1 to 9:16, but a video taller than 4:5 is cropped and centered to 4:5; the ad caption can run to 1,000 characters, with 80 to 160 recommended, and hashtags and URLs aren't supported in it.

Meta's rules are quoted from its Marketing API page Threads Ads Creation, read on 2026-09-27; the page warns that some updates to Threads ads are not yet available to all users. The Sume facts come from Video generation and Timeline 1.0.

What are the Threads ad specs?

The page gives shapes, caption rules, and placement rules. It lists no video length, file size, or minimum video resolution for Threads, and two of its lines disagree: it says hashtags aren't supported in the caption, and separately sets a limit of 30 hashtags per ad.

Which video shapes avoid the Threads crop?

Anything from 1.91:1 down to 4:5 escapes the 4:5 crop rule; taller video is cropped, and 21:9 (about 2.33:1, our arithmetic) is wider than the supported range. Generating a 1:1 or 16:9 clip is the simplest route:

• 16:9 and 1:1: in today's catalog code, the Seedance ids, kling-3, wan-3.0, minimax-h3, and minimax-h3-max list both. Check supported_aspect_ratios on GET /v1/videos/models before you submit.
• 4:5: not in the aspect_ratio values the docs list, and avatar video takes only 1:1, 3:4, 9:16, 4:3, or 16:9, so 4:5 comes from a render or a crop.
• 9:16 and 3:4: Threads crops them and centers the 4:5 window. If that's fine, deliver them as they are.

How do I make a 4:5 Threads video from a vertical clip?

Render it with Timeline 1.0, which takes only your workspace's media.sume.com URLs, such as a 9:16 clip you generated on Sume. Its output takes even edges from 256 to 2,160 px, so 1080×1350 is a 4:5 frame. With fit: "blur", the whole 9:16 clip stays visible and a blurred copy fills the sides instead of black bars, per the API reference; the default cover fills the frame and crops what overflows. Today a render's sound comes only from its audio spine, so detach the clip's audio and pass it as audio.url. Cropping a 4:5 window you position yourself is covered in Meta video ad specs.

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: threads-4x5-001" \
  -d '{
    "audio": {
      "url": "https://media.sume.com/artifacts/artf_demo/ad-audio.wav",
      "duration_seconds": 12
    },
    "output": { "width": 1080, "height": 1350 },
    "video": [
      {
        "source_url": "https://media.sume.com/artifacts/artf_demo/ad-9x16.mp4",
        "start": 0,
        "duration": 12,
        "fit": "blur"
      }
    ]
  }'

What goes in a Threads ad caption, and where does the ad run?

The caption is the ad's text, not subtitles burned into the video. Meta's page sets these rules:

• Over 1,000 characters, the ad is still created for Instagram but isn't delivered on Threads.
• Your Facebook Page information doesn't appear anywhere on a Threads ad.
• To deliver to Threads, the ad set lists both instagram and threads in publisher_platforms and must also select Instagram's stream placement, so the same creative runs in that Instagram placement too. Meta's Instagram and Facebook video specs are in Meta video ad specs.