Preview a 3-minute Short with 24 stills, one every 7.5 seconds

Short answer

A Short can run up to 3 minutes (read 2026-10-05), and POST /v1/video-frames takes at most 24 timestamps per call. 180 seconds divided by 24 is 7.5 seconds, so one call can show every 7.5-second window of a full-length Short. Put each timestamp in the middle of its window: 3.75, 11.25, and so on to 176.25.

Why a contact sheet beats scrubbing

A long vertical Short has a lot of places to go wrong: a clip that did not match its neighbor, a caption that cut off, a black frame at an edit point. Twenty-four stills in one look is faster than watching three minutes. Video frames decodes the accurate frame at each instant at the source size, with an optional max_edge clamp from 16 to 2160 and jpeg or png output.

The route accepts a source up to 300 seconds, so it covers the full Shorts length. It always returns 202 with a job, so you poll the job or the video_frames resource.

Spacing options

All rows use the 24-still cap per call.

Submit the call

The script builds the list and sends it. It asks for a 540-pixel long edge so the stills are easy to tile, and it sends an Idempotency-Key so a retry does not queue a second extract. Replace the URL with your own media.sume.com artifact.

import json, os, urllib.request

key = os.environ.get("SUME_API_KEY", "")
if not key:
    raise SystemExit("set SUME_API_KEY")
length, n = 180, 24
at = [round((i + 0.5) * length / n, 3) for i in range(n)]
body = {"video_url": "https://media.sume.com/artifacts/artf_demo/short.mp4",
        "at": at, "max_edge": 540}
req = urllib.request.Request(
    "https://api.sume.com/v1/video-frames",
    data=json.dumps(body).encode(),
    headers={"Authorization": "Bearer " + key,
             "Content-Type": "application/json",
             "Idempotency-Key": "preview-short-180"},
)
print(json.load(urllib.request.urlopen(req))["request_id"], at[:3], at[-1])

What to read in the stills

• Frame 1 and frame 24: the opening and closing beats. The last frame, 176.25 s, still sits inside the final window, not at the very end.
• Frames that look identical in a row: a clip held too long or a timeline slot that padded a short source.
• Text near the edges: whether burned-in captions survive in a 540-pixel view.
• Anything black: if you need the exact instant, request a denser at[] around that window.

Cost and limits

Video frames is billed by its own Modal compute rather than a flat per-job price, and the bill never exceeds the hold taken at submit. The docs I read give no flat rate, so check GET /v1/catalog before a large batch. For a coarser look at one clip, the default video inspect call returns 8 evenly spaced stills with a 768-pixel long edge and also gives you the probe, which is useful for checking duration against the 180-second ceiling before you spend the 24-still call.

If the source is longer than 300 seconds, trim the part you want first, then run this call on the trimmed clip.

For a quick sanity pass, sort the stills into a grid with any image tool and look for the three things that matter in a long Short: the hook at the start, a visible change every few windows, and a clean ending. If you find a problem at, say, the 9th still, the window is 63 to 70.5 seconds, which tells you where to open the edit.