Ensure that subtitles match the timing of on-screen activity
The display of subtitles should, as far as possible, match the onset and duration of the associated on-screen activity. Delays in either the onset or disappearance of subtitles can cause significant difficulties in following the programme. This is particularly important for dramas and other programmes with continuous changes of shot.
Studies show that viewers direct their attention to the subtitle area as soon as speech starts and may unnecessarily re-read subtitles that remain too long on the screen. Subtitles that appear or disappear very close to shot changes or that persist over unrelated scenes can cause considerable perceptual confusion.
For live subtitling using currently available methods, such as respeaking, it may be impossible to synchronise exactly. However, every effort should be made to keep the delays as short as possible. Delays of more than two seconds can cause significant difficulty, with longer delays making the subtitles impossible to understand.
Directions and techniques
Synchronise subtitles with programme sound
Subtitles should not lag behind the dialogue or commentary.
Subtitle appearance should coincide with the start of speech because this is when viewers will direct their attention to the subtitle area. Subtitle disappearance should coincide roughly with the end of the corresponding speech segment. This is because viewers may unnecessarily re-read subtitles that remain too long on the screen.
Synchronisation should occur at naturally occurring pauses in speech-sentence boundaries, or changes of scene.
Avoid overrunning shot changes
Avoid subtitles overrunning shot changes. Shot changes that take place while a subtitle is being read can cause the viewer to return to the beginning and re-read the subtitle.
If shot durations are short and changes frequent, it may not be possible to avoid overruns. In this case, at least ensure that the subtitle does not appear or disappear within one second either side of a shot change. ‘Anchoring’ the subtitle over a shot change by at least one second gives the viewer time to adjust to the new picture.
Avoid combining logically separate elements into one subtitle
There may be some circumstances in which two utterances or sounds are logically separate and should not be presented together in the same subtitle. An example is on a quiz show where a question or prompt is followed, a short time later, by the answer from a contestant. Viewers like to test their own skills by trying to answer the questions themselves, so the answer should not be displayed at the same time as the question.