Per second means five different things: how AI video pricing is actually billed

Nearly every AI video model now quotes a price per second of output. It reads like a unit you can compare — the way petrol is priced per litre — and it is not one. On a single rate card that prices a dozen models in the same currency, the meaning of "per second" changes five times.

Somebody trying to budget a series put the problem better than we can:

"Almost all WAN 2.5 i2v model vendors have incredibly tried to 'hide' API pricing compared to other models… I even reverse-engineered from Fal credit systems for like 20 mins just to figure out its pricing." — r/Qwen_AI

That is not a complaint about price. It is a complaint about arithmetic you cannot do, which is a different and more fixable problem.

The exhibit: one vendor, one unit, twelve models

Most price comparisons are assembled from a dozen vendor pages with a dozen different units, which is where the errors get in. Runway's developer pricing is more useful than any of them for one structural reason: it resells a dozen models — including wan3, veo3.1, seedance2_5, hailuo3 and gemini_omni_flash — and prices all of them in its own single unit, credits at one cent each.

It is a good yardstick before it says anything else, because it independently reproduces Alibaba's published Wan 3.0 rate to the cent: 5, 10 and 20 credits per second at 480p, 720p and 1080p, against Alibaba's own $0.05, $0.10 and $0.20.

And yet, inside that one rate card, the unit still shifts five times.

The five things "per second" means

1. A flat rate on output seconds

wan3 at 10 credits per second of 720p output. Six seconds costs 60 credits. Multiply and you are done. This is what everybody assumes the phrase means, and it is the minority case.

2. A rate with a floor under it

seedance2_5 is 20 credits per second at 480p — with an 80-credit minimum per generation. So:

The published rate is correct and the short clip costs double it. aleph2 carries a 56-credit floor and seedance2_mini a 64-credit one. The floor only bites on drafts — which is exactly when you generate most.

3. Output seconds plus input seconds

seedance2_5 at 720p bills 30 credits per second of output and 15 credits per second of input and reference video. A six-second output driven by a five-second reference clip:

output   6s × 30 = 180 credits
input    5s × 15 =  75 credits
                  ───────────
                   255 credits  ($2.55)

The per-second rate implies $1.80. The bill is 42% higher, and nothing in the phrase "thirty cents a second" told you. hailuo3 does the same thing and bills reference video at the same rate as output.

⛔ Wan 3.0 is not exempt from this one, and it would be convenient for us to imply otherwise. Reference-video seconds are billed at the output rate and count against the same thirty-second ceiling — it is written into this site's own spend model in as many words. Reference images, audio, documents and web pages are free; reference video is not. On the proportions, Seedance is actually the gentler of the two, charging input at half its output rate where Wan charges it at full.

4. Tokens, converted to seconds afterwards

Google's Gemini Omni Flash is not billed per second at all. It is billed per output token, and Google's pricing page supplies the conversion in a footnote: 5,792 tokens per second of 720p video, at $17.50 per million output video tokens.

5,792 × $17.50 / 1,000,000 = $0.1014 per second

Google rounds that to "approximately $0.10 per second" and the arithmetic agrees. But the invoice arrives in tokens, so nothing on it says "second", and a resolution change moves the token count rather than the rate.

5. A rate multiplied by a duration you do not choose

Veo 3.1's per-second rates are published plainly — Standard with audio is $0.40 a second at 720p and 1080p, Fast is $0.10, Lite is $0.05. What the rate does not tell you is that Google's own model page lists the duration options as 4s, 6s, 8s, and that 1080p, 4K and reference images require the 8.

So "$0.05 a second" on Veo 3.1 Lite is a real number attached to a menu. There is no five-second clip. If the shot wants 1080p, the model has decided your multiplier is eight.

The same clip, priced across the card

A six-second 720p clip with audio, read off Runway's rate card so the unit is constant:

At six seconds most of the floors do not bite and the column is close to honest. At two seconds it stops being honest, which is the length you use while you are still finding the shot.

What this does and does not say about Wan 3.0

It does not say Wan 3.0 is cheapest. On that card gen4_turbo is half its rate, and Veo 3.1 Lite at 720p matches Alibaba's 480p rate.

What it says is narrower and checkable: Wan 3.0 has no minimum charge, and the second you multiply is one you picked — any whole number from 2 to 30. Two of the five complications above do not apply to it. The third one does, and we have said so above rather than letting the omission do the work.

For a site's own pricing that translates into something you can verify without a calculator: a five-second clip here is 40 credits at 480P, 80 at 720P and 160 at 1080P — the rate doubles with each step up and the seconds are yours, so every other length is that number scaled. See the pricing page or what a clip actually costs.

What we could not verify

Kling's official developer rate is not in this article, and that is deliberate. Kuaishou's developer pricing page is login-gated and rendered in JavaScript; every per-second Kling figure we could find traces back to resellers or summaries rather than to Kuaishou. A pricing article that quotes a second-hand number next to five first-party ones is teaching the reader the wrong thing about all six.

The Sora 2 rates quoted around the web — $0.10 a second at 720p, $0.70 for Pro at 1080p — we did check against OpenAI's own pricing page, and they hold.

Questions

Why do two models with the same per-second price cost different amounts?

Because the unit is not the same unit. On one rate card pricing a dozen models, "per second" means five different things: flat output seconds, output seconds with a minimum charge underneath them, output plus input seconds, tokens converted into seconds, and a rate multiplied by a duration the model chooses for you. Two identical-looking rates can bill differently before you change a single setting.

What is a minimum charge on AI video, and when does it bite?

It is a floor the invoice cannot go below however short the clip is. Seedance 2.5 carries one, so a two-second 480p draft is billed at roughly double its own published per-second rate. Floors are invisible on the final cut and expensive during iteration, which is exactly when you generate the most clips.

Is reference material billed?

Usually yes, and on Wan 3.0 it depends on what the reference is. Reference images, audio, documents and web pages are free. Reference video is not: Alibaba bills those seconds at the output rate, and they share the same thirty second budget as the output. Seedance bills input video too, at half its output rate, which is proportionally cheaper than what we charge.

Does Wan 3.0 have the lowest per-second rate?

No, and the article says so. Other entries on the same card are cheaper. What Wan 3.0 has is no minimum charge and a duration you pick yourself, any whole number from 2 to 30 seconds, which makes it the rate on that card you can multiply and be right about.

The short version

• "Per second" is five different units. Flat output seconds; output seconds with a floor; output plus input seconds; tokens converted to seconds; and a rate times a duration the model picks.
• Floors only bite on short clips, which is when you iterate. Seedance 2.5 bills a two-second 480p draft at double its own published rate.
• Veo 3.1's duration is a menu — 4, 6 or 8 seconds, and 1080p forces the 8.
• Reference video is billed almost everywhere, including here. Reference images, audio and documents are free on Wan 3.0; reference video is not.
• The useful question is not which rate is lowest. It is which rate you can multiply and be right.