A caption that wraps into a paragraph is not a caption. It is a block of body text dropped on a moving picture, and on a 9:16 frame it will cover the face, hit the platform chrome, or both. Broadcast and streaming houses have used a band around 32–42 characters per line for Latin scripts for years; 42 is a widely used default, not a law the file format enforces. CJK scripts count glyphs differently and need their own cap.
Line length and reading speed are related but not the same lever. A 42-character line that stays on screen for half a second is still unreadable. A 70-character line that stays for four seconds is readable and still a layout problem on vertical video. Fix length first so the block has a shape, then check that the cue duration matches how long it takes to read that shape.
Auto captions will happily emit a 90-character cue if the speaker did not pause. That is the pass you do after transcription: split at a clause, not in the middle of a name. Versely's line-length checker loads an SRT or VTT and lists the offenders; it does not caption the video. The caption generator burns whatever transcript it has, so the split belongs in the transcript, not in a hope that the preset will wrap prettily.
In practice
- Cap Latin-script lines near 42 characters and two lines; split long clauses rather than shrinking the type until it fits.
- Never place a wrapped block in the bottom fifth of a vertical frame — that is where the platform UI sits.
- Names, URLs and product spellings are the strings that blow the cap; they are also the strings you must not hyphenate.
The mistake to avoid
Shrinking the font to keep a long line on one row. At phone size the line is still too long, and now it is also too small.
Where you will run into it
- AI Caption Generator — Drop a video, get timed captions. Free, on your device, no upload.
Related terms
Reading speed
Caption reading speed is how fast on-screen words arrive, in words per minute. A cue gone before it can be read is a timing error, not a style one.
Safe area
A safe area is the part of a vertical frame a platform's own interface will not cover — profile name, caption line, like and share buttons all sit outside it — and text or a face placed inside it is routinely hidden from the viewer entirely.
Burned-in captions
Burned-in captions meaning: subtitles rendered into pixels, so viewers cannot turn them off or lose them on re-upload. Closed captions are a separate track.
Caption timing
Caption timing is when each line appears and disappears relative to the speech — the clock, not the words and not the look.
Hook rate
Hook rate meaning: the share of people shown a video who are still watching a few seconds in. It grades the opening, not the body.
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