Paying for seconds you cut: generate 30 s, keep 12, on Sume video

Sume bills video by the output seconds you request, so a 30-second Wan 3.0 clip at 720p costs $3.75 even if you keep 12 seconds of it. The kept footage then costs $3.75 / 12 = $0.3125 per second, two and a half times the $0.125 list price. Ask for the length you will use, because duration is the one cost lever you control completely.

The unused-seconds table

Prices are per output second and linear in duration inside each model's valid range. The last column is the effective price of each second you keep.

Why people over-ask

Three habits cause it. Teams ask for the model's maximum so the edit has room. Teams ask for a long clip because it looks like better value per call. And a model's floor forces an overshoot: Seedance 2.5 bills a minimum of 4 seconds, so a 3-second moment costs 4 x $0.268677 = $1.0747 at 480p, an effective $0.3582 per kept second.

The first habit is the expensive one. A 10-second Omni Flash clip at 720p kept to 6 seconds costs $1.25 for $0.75 of use; the extra $0.50 buys cutting room that a 6-second request would not have had. That is sometimes worth it, but it should be a choice.

Splitting and stitching

Splitting does not save money, because the price is linear: one 12-second clip costs the same as three 4-second clips (12 x $0.125 = $1.50 on Wan 720p). It does cost extra jobs and a stitching step. A timeline compose is $0.02 and a render is $0.10 per output minute, so assembling three clips adds about $0.12 against $0 for a single clip.

So ask for the length you will use. If you do trim, the video trim job is $0.02, which is negligible against the generation line, but the seconds you cut were already billed.

A rule you can automate

Compute the duration from the script rather than choosing it by feel.

• Estimate spoken seconds from the script, add 1 second of lead-in and 1 second of tail, and round up to the model's step.
• Clamp to the model's valid range, such as 4 to 30 s for Seedance 2.5 or 2 to 30 s for Wan 3.0.
• If a shot needs only 3 seconds on Seedance 2.5, plan for the 4-second billing and use the extra second.

A budget line for it

Add a line called 'unused seconds' to your cost log. For a 30-second request that keeps 12 seconds on Wan at 720p, the line is 18 x $0.125 = $2.25 for that clip. Over 40 such clips it is $90.00 of generated footage that no viewer sees. Seeing it as its own number makes the habit visible, and a monthly figure is easier to argue about than a per-clip average.