A 60-second Seedance 2.5 piece: two 30 s jobs and one last frame

On Sume, a 60-second Seedance 2.5 piece is two 30-second jobs, with the second job starting from a still pulled from the end of the first. Together AI's page says Seedance 2.5 supports multi-round extension that keeps characters and pacing consistent across multi-minute videos, but that is the vendor's wording for its own endpoint. Sume's /v1/videos request table has no extend parameter, so extension is not something you can call there. Two 30 s jobs at 720p cost 2 x $17.34 = $34.68.

The handoff

Import the first clip with POST /v1/media-imports, then call POST /v1/video-frames with at set to a time just under the clip length, for example 29.9 for a 30 s clip. The value must be at least 0 and below the probed duration, or the worker fails with frame_time_out_of_range. The result is a durable PNG or JPEG at source size.

Send that image as frame_images with frame_type first_frame in the second /v1/videos job. Sume treats it as image-to-video, so the second clip starts from the same pose, framing and set. It does not carry the first clip's audio, motion or hidden state, which an extension feature may do; that is the main thing you give up.

Joining the parts

Use Sume's timeline to join the two clips into one MP4. Its plan endpoint is described as an unbilled preflight, so check the sequence there first. If the first frame of part two repeats the last frame of part one, trim a fraction of a second with video-trim, which Sume lists at $0.02 per job, so the freeze does not show.

Budgeting the two-job version

The second job needs a first frame, so the first job must be finished before you submit it. That makes the sequence serial: if each Seedance 2.5 job takes several minutes, the 60 s piece takes about twice as long as a single job. Sume lists callback_url on /v1/videos, so a webhook on job one can trigger the frame extract and job two without a poll loop.

Draft both halves at 480p first. A Seedance 2.5 30 s clip at 480p is $8.07, so a 480p draft of the full minute is $16.14, against $85.30 for the 1080p version (2 x $42.65). Wan 3.0 is $3.76 for the same minute at 480p (2 x $1.88) and $15.00 at 1080p, which is why it is the sensible choice for drafting a long piece before moving the final to Seedance.

Failed jobs are refunded, and a job can only be cancelled before generation starts, so submit job two only after you have looked at the extracted frame.

When extension would be worth chasing

• You need the same voice and sound bed across the join.
• Characters have to keep a pose or motion through the cut, not only an appearance.
• The vendor page makes this a headline feature, so test it on the vendor's endpoint before assuming it matches the handoff above.