One video, three rulebooks
Short vertical video is the one format that genuinely travels: film once, publish to Instagram Reels, TikTok and YouTube Shorts. But each platform enforces its own limits, and most failures are silent, the post goes up, then underperforms for a reason nobody tells you about.
The specs that matter
- Aspect ratio: 9:16 vertical everywhere. Full-frame 1080×1920 is the safe export for all three.
- Length: Shorts caps at 3 minutes; Reels and TikTok allow longer, but short-form ranking favors watch-through, TikTok says completion "would receive greater weight" (official For You explainer), and Instagram's Reels ranking predicts "how likely you are to watch a reel all the way through" (official statement).
- Watermarks: the big one. Instagram states on the record that it makes "low-resolution or watermarked reels" less visible (Instagram Ranking Explained, 2023; reinforced in its originality update). Always export the clean master from your editor, never re-download from a platform.
- Captions and text-safe zones: each app overlays UI at the top and bottom. Keep text in the middle band or it disappears behind buttons.
- Sound: licensed-music rules differ; a track that is fine on TikTok may mute your Reel. Original audio or platform-library tracks travel best.
The per-platform detail, with sources, lives in our free field guides: Instagram, TikTok and YouTube.
Publishing the trio without the tab dance
The workflow that holds up: export one clean 9:16 master, write the caption once, then adjust per platform, TikTok tolerates longer captions and more tags, Reels rewards a send-worthy hook, Shorts leans on the title. A scheduler that publishes through the official APIs, like ad2app, turns that into one composer pass instead of three uploads, and reports back which platform the video actually worked on.
Every claim above links its primary source. The per-platform specifics live in the free field guides, sources included.