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5 Digital Services

This document was originally published by the ITC, one of the organisations replaced by Ofcom at the end of 2003. It represents Ofcom’s current policy.

The advent of digital television offers the possibility of visual and technical enhancement of subtitles. One such way is the introduction of a clearer and more legible font and the use of symbols. The purpose of these changes is to increase the user’s enjoyment of television. They should not be introduced in a way which detracts from the prime purpose of the subtitling service, which is to facilitate the understanding of programmes by deaf and hard of hearing people.

The guidelines set standards on converting existing subtitle files for use on Digital Terrestrial Television (DTT). They also begin to set best practice for subtitles specifically prepared for DTT. It is not intended that these guidelines should inhibit future enhancements, but rather to control progress so that changes that deviate radically from current practice should be made only after careful consideration and consultation.

• The Tiresias font shall be used for all subtitles.
• The nominal size of subtitles shall be 24 television lines for the capital ‘V’.
• For reasons of latency use of intensive four-line subtitles, to include those within “add-ons”, shall be avoided. (Latency means the presentation of subtitles to the screen. Intensive subtitles mean those where the subtitle rows contain a considerable amount of text).
• Subtitles converted from existing EBU 3264 files or from pre-recorded live 335 tapes shall as closely as possible retain the positioning and line breaks of the original.
• The range of colours shall be limited to 12 that shall closely replicate the range associated with analogue teletext delivery.
• Line breaks on conventional aspect ratio receivers (4:3) and widescreen (16:9) receivers must retain the original emphasis of the subtitle.
• Subtitles shall be placed within the ‘Safe Caption Area’ of a 14:9 display. The location of text across the screen, which helps the identification of speakers, should remain intact.
• The present practice of using ‘#’ to indicate music shall be changed to use of two semi-quavers as part of the Tiresias set.

It is proposed that the veiling of either foreground or background may be used to prevent completely obscuring large areas of the background picture. This is a particularly useful feature when it is difficult to position the subtitles without obscuring vital picture detail. However, the effect of reduced contrast, and possibly legibility, must be considered when introducing veiling. The amount of veiling, which might be used, is currently under review.

An italicised form of text may be used to indicate emphasis within a subtitle.

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