App Store preview poster frame: default 5 seconds, check it

Apple's app preview specifications list the default poster frame as 5 seconds. To see what that frame looks like before you upload, call Sume video_frames on your rendered clip with at: [5]. It returns a still at the source size, and the call is unbilled.

Apple's figure is from its specifications page; video_frames behavior from the Video frames docs, read 2026-10-01.

How do I grab the frame at 5 seconds?

POST /v1/video-frames takes a video_url (a media.sume.com artifact or asset in your workspace) and exactly one of at[] or fps. Import the clip first with POST /v1/media-imports; there is no open-internet fetch.

curl -X POST https://api.sume.com/v1/video-frames \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: poster-check-001" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_demo/preview.mp4",
    "at": [5],
    "format": "png"
  }'

What do the options allow?

Can I compare more than one candidate?

Yes. at[] takes up to 24 values, so pass [3, 5, 7] to see the default next to alternatives. Every value must satisfy 0 <= t < duration, or the worker fails with frame_time_out_of_range; see that error explained. A 15-second preview, which is the shortest length Apple lists, has room for 5.

Does this choose the poster for me?

No. The extract shows what a 5 second frame looks like in your file. Choosing a different poster frame is done in App Store Connect, not in Sume, so check Apple's page for how that works today.