YouTube suggests 3 Shorts thumbnail frames: pick from 24 yourself

YouTube picks three suggested thumbnail frames for a Short on desktop, and you can pick another one on mobile. If none of those is right, extract up to 24 frames from your own clip with Sume video frames at the times you name, choose one, and upload it as the custom thumbnail. A call costs only the worker compute it uses, with no flat per-frame price.

What YouTube offers

On July 24, 2026, YouTube said YouTube Partner Program creators can upload fully custom thumbnails for Shorts, that desktop offers three suggested frames, and that mobile lets you pick any frame (YouTube Blog). The thumbnail help page lists 9:16 for Shorts, JPG or PNG files, and says Shorts thumbnails are edited in desktop Studio (YouTube Help). The blog and the help page differ on mobile, so check what your Studio shows. For a Shorts series, YouTube also lets you upload a distinct thumbnail for each Short (YouTube Help).

Pull candidate frames

POST /v1/video-frames takes one Sume-hosted clip and either an explicit at list (1 to 24 times) or an fps of at most 2, which is expanded to mid-bin samples and capped at 24. The source may be up to 300 seconds, which covers a 180-second Short. Frames keep the source size unless you set max_edge between 16 and 2160, and format is jpeg by default or png.

curl -X POST https://api.sume.com/v1/video-frames \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: ep4-thumb-candidates" \
  -d '{
    "video_url": "https://media.sume.com/artifacts/artf_ep4/ep4.mp4",
    "at": [1, 3, 5, 8, 12, 16, 20, 25],
    "format": "png"
  }'

Read the result

The submit returns 202. Poll the video_frames resource until resource_status is ready, then read frames[{t,url,width,height}]. A frame that fails shows url: null and does not fail the whole job.

Compare what each tool gives you.

Pick and upload

Ask for a PNG when you plan to add text or a crop, then export the final as JPG or PNG at 9:16. For a whole season, run one call per episode and keep the winners in one folder. A frame from the video itself is also the safest match to what the viewer will see after tapping. Custom Shorts thumbnails are limited to YPP channels for now, so a channel outside the program should still check its first frame; the post on pulling the frame for each episode covers the series workflow.