Ensure that subtitles are easy to read
Viewers will need to be able to read and understand the subtitles at the same time as taking in the action on screen. There is a lot of information to process. While a subtitle is displayed, the entire scene must be viewed including all objects, activities and interactions. To make sense of the subtitles the speaking characters’ facial expressions must also be analysed. In order to be sure of their interpretations, viewers often need to flick their visual attention back and forth between the subtitles and the visual scene, sometimes re-reading parts of a subtitle. This all takes time and mental energy. Viewers may give up on programmes if they involve too much effort.
Subtitles must therefore be well written and presented in a way that makes reading and understanding them easy. One of the biggest challenges is in allowing for a reading speed that displays the subtitles for long enough to ensure that all viewers have enough time to read them. Reading speed is a complex issue. It is affected by the quality of the subtitles, the amount of action on screen and the complexity of the subject matter. The maximum reading speed that a person can achieve will also vary according to their age their level of literacy in the subtitle language, the extent to which they rely on the subtitles, their familiarity with subtitles, their familiarity with the programme or genre and even the time of day, because this affects their alertness and concentration level.
Directions and techniques
Ensure subtitles are in standard readable language (high priority)
Without unnecessarily altering the meaning or the words that are spoken, write the subtitles in normal written language, using standard punctuation.
For children, take account of the reading age and reword or reduce the text accordingly.
Present subtitles in blocks, not word-by-word
Subtitles should be displayed in blocks, rather than one word at a time. A subtitle that is displayed one word at a time will take longer to read than the same subtitle displayed all at once as a block.Studies carried out within the DTV4All project concerning subtitles for people who are deaf or hard of hearing show that word-by-word subtitles cause very chaotic reading patterns requiring almost twice as many visual fixations as block subtitles. Fast readers may experience problems due to ‘getting ahead’ of the subtitles and casting their eyes on gaps where no word has been displayed. This leads to poorer comprehension compared with block subtitles.
For live subtitles, the situation may not be as clear. Waiting for text segments to be complete may exacerbate the problems caused by the delays inherent in creating live subtitles.
Start and end subtitles at natural, logical points (high priority)
Subtitles should end at natural linguistic breaks, preferably sentence breaks. To reduce reading time, two or more short sentences can be combined into a single subtitle.
Very long sentences that are too long to fit into a single subtitle can be broken into two or more pieces using ellipsis (‘...’) or reworded to form two or more separate sentences and displayed as consecutive subtitles.
Choose line breaks within a subtitle carefully
If a subtitle contains more than one line of text, a number of considerations should be used to determine where best to put the line breaks:
- Each line should end at a natural linguistic break.
- Line breaks should minimise the distance the eye has to travel from the end of one line to the beginning of the next. This means that breaks may be different for left justified, centred, or right justified subtitles of the same text.
- If left justified, centred and right justified subtitles are used together (for example to distinguish each speaker when subtitling a conversation), line breaks can be used to better distinguish between them, by creating shorter lines.
- For centred or right justified subtitles, avoid very short phrases on one line followed by very long ones on the line below, otherwise the second line may be read first.
- Line breaks can be positioned to avoid disrupting the background picture.
Allow adequate reading time
For example, English language subtitles for a general audience should not usually exceed 170 words per minute and, if possible, be kept to a maximum 140 words per minute. These limits apply to individual subtitles. Even if the average is achieved over a longer time period, short bursts of dialogue or complex multi-speaker scenes exceeding this limit may cause problems for viewers. The BBC online subtitling editorial guidelines contains a useful guide to English language timings for example sentences of different lengths.
This may vary for different audiences. For example, for many pre-lingually deaf children, experiments suggest that a presentation rate of 70-80 words per minute is best for English language subtitles.
Allow extra time if the subtitles contain unfamiliar words, long numbers or labels or if the scene contains several speakers, shot changes or a lot of action or detail to take in.
Use a clear visual presentation (high priority)
Subtitles should appear within the title safe area. That is the visible area where the text will not be cut regardless of the over scan (margin of the video image that is normally not visible) of the television used
Use a screenfont designed for viewing subtitles on television displays at typical TV viewing distances.
Avoid scrolling or moving text as this can be difficult for some viewers to focus on.
Use mixed case lettering, except for label prefixes and other special cases.
For the display of subtitles, make sure the text contrasts well against the background. The most legible colour combinations are blue on white, white on blue, red on white, white on red, cyan on blue and blue on cyan. Use colours with a saturation index of less than 85% to avoid distortion and flicker.
Consumer equipment can give users the option to change the text presentation such as size, colour and background colour. It is useful to provide a number of preset options, including a high contrast option. However, size changes should never result in text being outside the visible area.
Position subtitles to avoid obscuring important content
Avoid obscuring any burnt-in subtitles or scrolling news tickers.
Avoid obscuring any part of a speaker’s mouth.
Avoid obscuring any important activity. For example, the usual position for subtitles, at the bottom of the screen, may not be appropriate for a sport like snooker where the most important activity often occurs around the black ball, which is at the bottom of the screen in the common overhead shot.