Length is the biggest divergence
TikTok allows up to ten minutes, Shorts up to three, and a Reel up to ninety seconds. A single cut sized for TikTok will simply be rejected or truncated elsewhere.
The practical approach is to edit the longest version first and trim down, rather than trying to stretch a ninety-second cut into something longer.
Safe zones differ more than people expect
TikTok and Reels both cover roughly a third of the bottom of the frame with captions, the audio label and the action buttons. Shorts is considerably lighter, reserving mainly the subscribe row and progress bar.
That means text placed for Shorts will be buried on TikTok. Design for the most aggressive overlay - TikTok or Reels - and it will be safe everywhere.
Text fields are not equivalent
TikTok and Instagram give you a caption of about 2,200 characters and nothing else. YouTube Shorts gives you a separate 100-character title plus a 5,000-character description, and the title is indexed by YouTube search in a way the others are not.
Shorts is therefore the one place where keyword-aware titling genuinely affects discovery beyond the recommendation feed. Reusing the same caption across all three wastes that.
Sound behaves differently
All three autoplay with sound in-feed, unlike LinkedIn or X. But burned-in captions still matter, because a large share of viewing happens muted by choice.
Trending-audio mechanics are strongest on TikTok, weaker on Reels and largely absent on Shorts, where the recommendation is driven more by watch-through than by sound.
The short version
One 9:16 master, framed for the TikTok safe zone, trimmed to ninety seconds for Reels, and given a real keyword title on Shorts. That covers all three without three separate edits.