LinkedIn event cover at 1280x720 and the promo post video

LinkedIn's event cover must be 16:9, and the help page names two sizes: 480x270 or 1280x720. 1280x720 is also a size ChatGPT Image 2.5 accepts through Sume, so you can generate the cover directly and download it. LinkedIn then asks you to write a short post to promote the event, and a 15-second video from Sume Timeline makes that post stronger than text alone.

What does LinkedIn require for an event?

The event help page says the cover image can be 480x270 or 1280x720 pixels, with a minimum width of 480 and a 16:9 aspect ratio. Images stored in the cloud cannot be uploaded; you upload from your device. Events are online or in person, with a format of LinkedIn Live or an external event link. After you create the details, you write a short post to promote the event, and once you post, the Organizer, Event type and Event format cannot be changed.

How do I generate a 1280x720 cover?

Request openai/gpt-image-2.5 with image_size set to "1280x720". The smaller 480x270 size is outside the GPT rules, so use 1280x720. Fix the text in the prompt carefully, because a cover with a misspelled event name is hard to rescue; for text-heavy covers see how Sume's image notes treat quoted copy.

curl -X POST https://api.sume.com/v1/images \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: li-cover-001" \
  -d '{
    "model": "openai/gpt-image-2.5",
    "prompt": "Clean 16:9 event cover, speaker silhouette on a stage, bold title text \"Pricing Workshop\"",
    "image_size": "1280x720"
  }'

Why can't I paste the Sume link into LinkedIn?

LinkedIn says cloud-stored images cannot be uploaded, only files on your device. Sume returns a media.sume.com URL, so download the file from that URL to your device, then upload it. The same goes for the video you attach to your promo post.

How do I make the promo post video?

Build a 15-second 16:9 clip: the event title card as a still slot, then two or three slots for speaker photos or venue shots. Set output to 1920x1080 and the audio.mode to silence, then add the date and time as cues captions. LinkedIn locks the Organizer, Event type and Event format once you post, so settle those before you publish, and write the post copy to match the video: one line on what, one on when.

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: li-promo-001" \
  -d '{
    "audio": { "mode": "silence", "duration_seconds": 15 },
    "output": { "width": 1920, "height": 1080 },
    "video": [
      { "source_url": "https://media.sume.com/artifacts/artf_c/cover.png", "start": 0, "duration": 5 },
      { "source_url": "https://media.sume.com/artifacts/artf_p/speaker.jpg", "start": 5, "duration": 10,
        "transition": { "type": "dissolve", "duration": 0.5 } }
    ]
  }'

What should I proof before publishing?

Check the title, date and time zone on the cover and in the video cues against the event page, and confirm the format (LinkedIn Live or external link) is the one you will use, since it cannot be edited after the promo post goes out. A cost note: a 15-second Timeline render is $0.10, and the image is priced by the catalog for the model and quality you pick.