How to add captions to a vertical video

To add captions to a vertical video, show them one short line at a time, timed to the spoken words, and keep every line off the speaker's face and above the strip the phone covers with its own buttons. Then read every caption word against the audio before you post, because a caption that looks fine can still be wrong.¹²

How should captions be split into lines?

Split them by time, not by a fixed number of words. Fixed word counts are the main reason automatic captions read as machine-made: the breaks ignore how the person speaks, so a line stops mid-phrase and lingers for no reason. Break a line at a pause, at the end of a sentence, or when it gets too long, whichever comes first.³

Keep each line on screen for about 0.83 seconds at the least, or it flashes past before anyone can read it.³

Where should captions sit on a vertical video?

Low enough to stay out of the way, and high enough to clear the phone's own interface. TikTok, Reels and Shorts draw the username, the post caption, the music line and the action buttons over the bottom of the video, and anything in that strip is partly covered. On a 1080 by 1920 frame we keep captions at least 320 pixels up from the bottom, and check it on the finished frame rather than trusting the arithmetic.²

Never put a caption over a face. When a line would cross the speaker's face, move it below the chin if it still fits above the speaker's name line, and above the eyes if it does not.¹

Why do captions sometimes hang over silence?

Because one word was timed late, and the line waits for it. We once saw a single short line sit on screen for 22 seconds over silent footage because its last word had been placed 22 seconds late. The fix is to break a line at any gap of more than one second between its words, and to treat any word that still lands in the wrong place as a timing error to correct by hand.¹

How do you make captions easy to read?

Size the text by how tall the capital letters actually look, not by the font size number, because the same size reads very differently from one typeface to the next. Use a pure black outline: a grey one disappears against bright backgrounds. If you set captions in capitals, add a little space between the letters.³

Leaving any caption setting at the software's default is what produces the home-video look, so choose every setting on purpose.³

How do you get the words and punctuation right?

Check every caption word against the audio before posting. In one of our clips, "those words" came out as two separate captions reading "THOSE" and "OH", and it passed a look at the frames. Only reading each word against a second, independent transcription caught it. Keep a list of the names and terms the speaker uses, so they are spelled the same way every time.¹

When the speaker gives you their own text, such as a script or an approved transcript, let it decide the punctuation, capitals and spelling, but not which words were said. The audio still decides the words. Add or correct punctuation from their text; never strip a mark because their text left it out.⁴