The short definition
A cue is one block of timed text. It has three essential parts: a time when it appears, a time when it disappears, and the words to show in between. A subtitle file is a list of these blocks in order. When people talk about “a subtitle” on screen, they usually mean one cue.
You may also hear the same thing called a caption block, a subtitle event, a frame of text or simply a line. Terms differ between tools and file types, but the idea is the same.
What is inside a cue
Most cues contain:
- A start time: the moment the text appears.
- An end time: the moment the text is removed.
- Text: one or two lines of words, sometimes more in unusual cases.
Many formats also allow an identifier, such as a running number, which makes it easier to refer to a particular cue. Some formats add optional information such as position on the screen, alignment, or styling like italics. Not every player respects these extras, so basic cues with plain text are the safest.
Here is a hypothetical cue written in plain language: appears at 1 minute 5 seconds, disappears at 1 minute 8 seconds, shows the words “We should leave before it gets dark.” The three seconds in between is its duration.
How cues relate to speech
A cue usually matches a natural chunk of speech: a short sentence, a clause or a phrase. People who write subtitles try to cut at points where the meaning breaks naturally, so a viewer reads a complete thought at a time. A long sentence is often split across several cues. A very short utterance, such as a single word, may be a cue on its own or may be joined with its neighbors if the timing allows.
One cue is not the same as one line. A cue may hold two lines, stacked one above the other, and they appear and disappear together. This is why the two-line limit is a limit on a cue’s content, not on how many cues can follow one another. Decisions about how to split a sentence across subtitle lines happen inside a cue, while decisions about where to start a new cue come from timing and meaning.
Why cues are the basic unit
Everything about timing is organized around cues. A reviewer checks each cue’s duration, its reading speed and the gap before the next one. A translator usually works cue by cue, so the translated text has to fit the same time slot as the original. A player shows or hides each cue as playback passes its start and end times. Editing tools let you move, split and merge cues, which are the three operations that account for most of the work in adjusting subtitles.
Because the cue is also the unit that tools count, many quality checks are expressed in terms of cues. They ask whether any cue is too short, too long, too crowded or too close to the next. Such checks are helpful, but they are only a guide and need a person to judge the borderline cases.
Cue length and the reader
Cues come in many lengths. Very short ones, lasting under a second, are hard to read and can seem to flash. Very long ones can stay on screen after the speaker has moved on, and may cover the picture for too long. Most guides sit somewhere between: long enough to read comfortably, short enough to match the speech. The exact limits vary between guides and languages.
The amount of text in a cue matters too. A cue that holds more characters than a viewer can read in the available time will feel rushed. Writers then use text condensation to shorten the wording, or they extend the time when the audio and picture permit.
Cues and gaps
Between one cue and the next there is either a gap or none at all. A tiny gap can help the eye notice that the text has changed, which is useful when two cues look alike. When cues touch with no gap, a quick change can be easy to miss. Tools often include a setting for the smallest allowed gap between cues, and specifications from clients or broadcasters may set one.
Overlap and simultaneous speech
In ordinary subtitles, cues follow one another in sequence. Sometimes two people speak at once, and the writer must choose: show both in one cue with a clear indication of who is speaking, or prioritize the more important speaker. Overlapping cues, where one starts before the previous has ended, are supported in some formats but handled badly by some players, so they are usually avoided in simple deliveries.
Cues in live subtitling
Live captions also appear as units of text, but they are produced as people speak, so the cue boundaries come from the captioning method and not from careful editing. The result may scroll or build up word by word. The idea of a start time and an end time still exists underneath, though the viewer experiences it differently.
Seeing cues for yourself
If you open a plain text subtitle file in a text editor, you will often see cues directly: a number, a line with two times separated by an arrow-like symbol, then the text, then a blank line before the next one. Another way to see them is in a subtitle editor, where each cue appears as a row or a block along a timeline. Looking at a few examples is the quickest way to understand how a simple list of timed text can drive everything you see on screen.