Day-to-night time-lapse from two photos on Seedance 2.5: 8 s, $4.62

A day-to-night time-lapse from two photos costs $2.15 at 480p, $4.62 at 720p and $11.37 at 1080p for 8 seconds on Seedance 2.5 (16:9). The daytime photo goes in as first_frame and the night photo as last_frame (read 2026-10-09).

Cost of the transition

Seedance 2.5 lists first_frame and last_frame in its supported frame images. The price is the same token formula as any other Seedance 2.5 job: resolution, seconds and aspect ratio.

Body

frame_type is required on each entry. A last_frame without a first_frame is rejected.

import os, time, requests

API = "https://api.sume.com/v1/videos"
H = {"Authorization": "Bearer " + os.environ["SUME_API_KEY"]}
body = {"model": "seedance-2.5", "prompt": "Time-lapse of a harbor from midday to night, clouds streaking, lights turning on", "duration": 8, "resolution": "720p", "aspect_ratio": "16:9", "frame_images": [{"type": "image_url", "image_url": {"url": "https://example.com/harbor-day.jpg"}, "frame_type": "first_frame"}, {"type": "image_url", "image_url": {"url": "https://example.com/harbor-night.jpg"}, "frame_type": "last_frame"}]}
job = requests.post(API, headers={**H, "Idempotency-Key": "harbor-lapse-001"}, json=body, timeout=60).json()
deadline = time.time() + 1800
while time.time() < deadline:
    time.sleep(30)
    job = requests.get(job["polling_url"], headers=H, timeout=60).json()
    if job["status"] == "completed":
        print(job["unsigned_urls"][0], job["usage"]["cost"])
        break
    if job["status"] in ("failed", "cancelled"):
        print(job["status"], job.get("error"))
        break

A shoot of twelve locations

Twelve locations with two photos each and an 8-second 720p lapse cost 12 x $4.62 = $55.47. At 480p the set costs $25.79, and at 1080p $136.47.

Send the same aspect_ratio for every location so the finished clips line up in one timeline. Seedance 2.5 accepts 21:9, 16:9, 4:3, 1:1, 3:4 and 9:16.

For the test round, use 480p. The lapse concept is clear at low resolution: if the light and clouds read well in a 480p draft, they will at 1080p too.

Checks

• Shoot both photos from the same tripod position. The model blends between frames, and a moved camera shows up as a morph.
• The aspect ratio of the output should match the photos; send aspect_ratio explicitly.
• Frame images are for exact start and end frames. Style references go in input_references and do not set the frames.
• Length is a pace choice: 8 seconds costs $4.62 at 720p and 12 seconds costs $6.93; pick the one that suits the cut.