AI video for social media: sizing, length, and posting tips for Reels, TikTok, and Shorts

Reels, TikTok, and YouTube Shorts are all built around a vertical 9:16 frame — a landscape clip gets letterboxed with dead space on both sides, which reads as low-effort no matter how good the generation itself is. Set the aspect ratio to portrait before you generate rather than cropping afterward, since cropping a landscape composition after the fact often cuts off the subject the shot was actually built around.

Short-form platforms consistently reward clips that get to the point fast — the first one to two seconds decide whether someone keeps watching or scrolls past. A single clear beat (one action, one reveal, one punchline) at 5–10 seconds usually outperforms a longer clip trying to tell a whole story, unless you're specifically building a multi-scene narrative, in which case stitching several short generations together beats one long uncut clip.

A model's native audio is useful for ambient sound and sync'd motion, but most short-form platforms live and die by trending audio, not ambient sound. For anything you're posting to perform (not just to showcase), it's usually worth generating without audio and adding a trending sound in the platform's own editor afterward, so the clip can actually ride that trend's reach.

A large share of short-form video is watched muted, especially on the first few seconds before someone decides to unmute. If the clip depends on dialogue, on-screen text, or a spoken hook to land, add burned-in captions in your platform's editor before posting rather than assuming the visual carries it alone.