“You want a 6-second video because that's one ad format in YouTube. You want a 10 to 15 second video. Around 20 seconds is great for YouTube Shorts. 30 seconds or longer is probably going to serve in-stream as a skippable ad. You have to have a lot of variety in terms of lengths on Google — compared to Meta where you mostly see a 15- or 20-second Reel.”

Video assets need multiple lengths for YouTube: 6s, 10-15s, 20s for Shorts, 30s+ for in-stream

YouTube alone has at least four distinct ad inventory formats (bumper, non-skippable, Shorts, in-stream skippable) with very different optimal video lengths. Most UAC advertisers upload one or two video lengths and wonder why performance is inconsistent. A proper video asset library covering all four duration buckets gives the algorithm more surface area to match ad format to inventory type.