The short answer
Use Fast Recast when iteration speed and volume matter most: clear single-subject motion, a well-matched character image, and several variations you want to compare quickly. Use Preserve Scene when the shot depends on harder details such as prop contact, occlusion, camera movement, or a character that turns across multiple angles.
That is a workflow rule, not a universal quality claim. Run the same short source through both modes when a shot is commercially important, then compare cost per usable output instead of choosing from technical branding.
Where Fast Recast is strongest
Fast Recast is designed for repeatable character and motion testing. Saved character assets and a consistent source let a team create several comparable variations without rebuilding the setup for every attempt.
It is the practical default for clear source motion, fast creative exploration, and batches where the goal is to find a promising character-and-shot pairing before investing in more demanding preservation.
Where Preserve Scene is strongest
Preserve Scene is built for shots where identity consistency must survive multiple angles, expressions, face occlusion, hand-to-object contact, or visible camera movement.
It works best when the character reference matches the source framing, the subject remains visible, and the source is a continuous shot with moderate motion. Treat it as the deliberate choice for difficult shots, not the automatic choice for every batch.
Choose by failure risk, not prestige
A simple full-body dance or gesture is usually a good Fast Recast candidate. A seated shot with a bottle crossing the face, a hand gripping an object, or a camera that reframes the subject is a better Preserve Scene candidate. ClipRecast keeps those choices outcome-first and handles the technical route behind each mode.
For either mode, bad input matching can dominate generation quality. Match the character reference to the source pose and crop, avoid cuts, keep enough space around large movements, and test three to five seconds before scaling a long clip.
How batch economics change the decision
Fast Recast is well suited to four- or eight-output exploration batches. Preserve Scene is better treated as a focused mode for shots where difficult scene details justify the higher quote, or as a second stage after an exploration batch identifies a promising pairing.
Quote the whole batch before submission. Reserve the total atomically, show the average credits per output, then reconcile each output independently so confirmed technical failures return only the eligible portion.
A practical two-mode test
Start with one rights-cleared three-to-five-second source and one saved character. Run four Fast Recast outputs, score identity, hands, object contact, background, and first-to-last-frame continuity, then use Preserve Scene only when the scorecard shows that scene preservation is the limiting factor.
Keep the winner as a reusable recipe. The next batch should change one variable—character, source crop, or generation mode—so the additional spend creates evidence instead of a folder of unrelated clips.
This guide describes a product workflow and general information; it is not legal advice.