What AI video generation costs
AI video is priced per second of output, multiplied by the model you chose — which is why apps sell credits rather than a flat number of videos, since a long clip on a premium model can cost twenty times what a short one on a cheap model does.
Why credits and not videos
The cost of a generation to whoever runs the app is a rate per second charged by the model provider. A ten-second premium clip and a three-second cheap one are not remotely the same purchase, so "ten videos" would be meaningless as a unit.
Credits make the two variables visible at the point where you choose them: pick a longer duration or a better model and the price in front of you goes up before you commit.
The two levers
Duration, which is close to linear. Half the length is close to half the cost.
Model, which is a large multiplier. The spread between the cheapest and the most expensive per second is more than tenfold.
Spending fewer of them
Test short and cheap. Most wasted credits go on long premium renders of a photo that was never going to work.
Fix the photo before changing the model. It is free.
Buy in whichever shape matches your use: a pack if you generate in bursts, a subscription if you generate steadily.
A note on failures
Credits should be committed on completion, not on submission — a generation that fails should leave your balance untouched. If it does not, that is a bug worth reporting rather than a policy.