Choose 15 seconds for UGC-style try-on ads aimed at cold audiences — the hook decides performance in the first 1.5 seconds, and extra runtime adds nothing there. Choose 30 seconds when the ad carries real story load: multiple looks, fabric detail, or a promo offer that needs register time. At roughly $75–$530 per AI-produced fashion ad, the strongest move is producing both lengths and letting performance data pick.
Match the length to the format, not the other way around. Documented fashion campaign specs recommend 15 seconds for a UGC try-on ad and 20 seconds for a cinematic editorial fashion film — a 30-second cut only earns its runtime when it carries genuine story load. One documented 30-second fashion montage used that time to show 4 characters wearing multiple fabric weights; a single-look try-on has no equivalent job for the extra 15 seconds.
Don't cut below what the creative actually needs. In one documented production, the invideo agent — invideo is an agentic video creation tool that plans and generates the ad from your brief — pushed back on a 15-second request and recommended 20 seconds to preserve the hook beats and give the promo offer time to register. The reverse also holds: length never rescues a weak opening. The scroll-stopping window for a performance ad is about 1.5 seconds, and the first 3 seconds decide how a UGC-style ad performs, so concentrate iteration on the hook before debating 15 versus 30.
Budget for the production difference between the two lengths. Video models cap each generation at around 15 seconds (Seedance 2.0's hard limit), so a 15-second ad can render as a single multi-shot pass, while a 30-second ad is assembled from multiple generated segments stitched in a timeline. The cost gap in documented productions reflects that: a 20-second product film ran about $75 (300 credits, 25 clips generated), while a 30-second multi-character montage with heavy iteration ran about $530 (2,100 credits). Longer means more segments, more iteration, more rejected clips.
If you're running paid traffic, produce both lengths and let the platform decide. You can't predict the winner without shipping it, and at these production costs an A/B test is cheaper than a wrong guess: build the 30-second master first, cut a 15-second version from its strongest beats, run both, and scale whichever holds ROAS. Because the invideo agent keeps your brand context, shot styles, and locked characters in project memory, the second cut is largely re-assembly — in one documented run, the second ad in the same project came out 33% faster because zero context setup was needed.
Watch some of these to see what works for you:
In the old world, you'd have to guess which one's going to win and then just ship that, but now with this workflow, you can ship all of these in parallel and just scale the one that actually performs.
— invideo's creative team