Subtitle formatting rules

Lines and length

• Two lines maximum. A third covers too much picture and takes longer to read than the subtitle usually stays on screen.
• Professional practice puts a line at somewhere in the high thirties to low forties of characters. Narrower frames and larger text push that number down.
• When a subtitle has to be two lines, a roughly balanced pair reads faster than a full line followed by a stub.
• Never split a word across lines. Never split a name, a number and its unit, or a phrase that is read as one thing.

Where a line should break

The break should fall at a natural pause in the sentence. Breaking after a comma or between clauses keeps each line a coherent chunk. Breaking between an article and its noun, between a preposition and what it governs, or between an adjective and the thing it describes forces the reader to hold half a phrase in mind while the eye travels, and that costs time.

Languages written without spaces between words, such as Chinese, Japanese, and Thai, do not get to lean on spaces at all. The break has to be chosen by meaning, which is why naive automatic wrapping produces such poor results in those scripts.

Placement

• Bottom centre by convention, because that is where viewers look for it and where it covers the least important part of most compositions.
• Leave clearance at the very bottom of the frame. Player controls, platform overlays, and safe-area insets on phones all live there.
• Move a subtitle up temporarily if it would cover something that matters, such as on-screen text or a face doing the talking.
• In vertical video the contested zone at the bottom is much larger, since interface elements take a bigger share of a narrow frame.

Punctuation and case

• Sentence case. Setting subtitles in all capitals slows reading measurably, because word shape is part of how people recognise words.
• Keep punctuation that helps parsing and drop punctuation that only adds characters. A comma that marks a clause boundary earns its space; a trailing period on a line that ends mid-sentence does not.
• Use an ellipsis sparingly, for genuine trailing off rather than as a continuation marker on every split sentence.
• Follow the target language's own typographic rules rather than English ones. French wants a space before certain punctuation, Spanish opens questions with an inverted mark, and Chinese and Japanese use full-width punctuation.

Contrast and legibility

• Text needs to survive whatever is behind it. An outline or a shadow keeps white text readable over a bright background without a solid box.
• Size for a phone, not for the screen you are editing on. Most viewing happens on the smallest screen you tested on, if you tested on it at all.
• Scripts with marks stacked above and below the line, such as Thai, Vietnamese, and Devanagari, need more line height than Latin text at the same size.