Wan 3.0 duration -1 (smart length) vs Sume's whole seconds

Alibaba's Wan 3.0 pages accept a duration of 2 to 30 seconds or -1 for smart length, with 5 seconds as the guide's default. On Sume, duration is an integer in seconds and the wan-3.0 row accepts 2 to 30, so there is no smart value to send. Pick the length in your own code before you submit.

How do the two compare?

The range matches; the smart value does not exist on Sume.

What does an explicit length cost?

At 720p, Sume's Wan 3.0 rate is $0.125 a second (fal's list of $0.10, read 2026-10-09, x 1.25; fal). Length decides the price, so a 5-second clip is $0.625 and a 12-second clip is $1.50. A smart length would hide that number from you until the job finished; an explicit one lets you budget before you submit.

How do you map a requested length to a supported one?

Read supported_durations from GET /v1/videos/models, then snap to the nearest value. The function refuses -1 so a ported body cannot slip through.

def pick(requested: int, supported) -> int:
    if requested == -1:
        raise ValueError("send a whole number of seconds, not -1")
    return min(supported, key=lambda s: (abs(s - requested), s))

supported = range(2, 31)
print(pick(7, supported), pick(40, supported), pick(1, supported))

What if you need more than 30 seconds?

Split the story into shots and join them. Sume's Timeline is the documented way to assemble clips.