Smalltown Boy 舞蹈换人教学。同一条竖屏双人舞，按硬切拆成前段 14 秒和后段 7.17 秒，分别换人生成，再截取、合并成 21.17 秒成片。
Smalltown Boy dance recast lesson. One vertical duet is split on the hard cut into a 14-second clip and a 7.17-second clip, recast, trimmed, and joined into a 21.17-second film.
界面有中文和英文。提示词保持原文。