ITU-R REPORT BT.1080-1 PDF

Introduction

This Report considers the methods used in the international exchange of television programmes which contain data-encoded captions (sub-titles).

These considerations relate to the work of Study Group 11 but methods of international exchange include television magnetic tape recording, satellite and long-distance transmission links. It will therefore be necessary to inform the CMTT and Study Group 10 of this work and, where necessary, refer questions to them. Such questions may include the choice of line numbers in the field-blanking interval for captions.

Further information on captions and teletext services can be found in Report 802 and on teletext systems in Recommendation 653.

Usually, the caption data is according to one of the teletext systems although in North America a low-speed method, using Line 21, developed by the Public Broadcasting Service (PBS) [Lentz et al., 1978] is also in widespread use.

These "closed" captions are displayed, at the viewer's choice, with the picture by means of a special decoder associated with the receiver. Captions are usually in the language of the programme and intended as a service to persons with impaired hearing. Captions may be provided in languages other than the programme sound, or in the case of special educational programmes, explanatory text or graphics may be used. The use of captions is expected to increase, especially multi-language captions in the case of direct satellite broadcasting.

Captions are an integral part of the programme. Caption data can be broadcast in the field blanking interval, either confined to certain lines or included within part of a total teletext package which contains other material not related to the programme.

Methods of caption exchange include the use of several different types of computer floppy discs. The caption data on these discs is related to the programme videotape using the SMPTE or EBU time-and-control code, details of which are available in Reports 630 and 963.