7 The subtitling of television programmes

Teletext allows the transmission of subtitles (or captions) that need to be displayed only as and when required. Subtitles transmitted in this way are referred to as ‘closed captions’ whereas subtitles inserted as a video signal into the programme video are called ‘open captions’. Teletext subtitles are of obvious benefit to viewers with hearing impairments. They may also be used to make available simultaneously subtitles in several different languages, by transmitting them on different pages. Preparation of subtitles for transmission with a prerecorded programme is a very time consuming process but the use of microprocessors and software incorporated into specially designed preparation systems has reduced the time required from about 30 hours to some 10-15 hours per programme hour.

Figure 7.1 Subtitle recording system for regional teletext service

Subtitling of prerecorded programmes

Subtitles for prerecorded programmes are prepared in advance of transmission and stored on floppy discs. The subtitle editor would normally have the programme to be subtitled available as a tape recording together with a programme script. This tape ‘dub’ of the programme master tape will also have the studio time-code reference which is used for programme production purposes. The time-code can therefore be used to key the subtitle ‘on’ and ‘off’ times. Subtitling takes place separately from programme production and also separately from the technical and editorial procedures concerned with the provision of a teletext service. Subtitle preparation can therefore be undertaken with purpose-designed work stations in a separate location.

The functional diagram of a typical station is shown in Figure 7.1. The programme to be subtitled would normally be viewed from a tape dub with time-code copied from the programme master tape. A subtitle script would normally be prepared by manually editing the programme script to a reading rate of about 100 to 120 words per minute. In preparing the subtitle script, key words of utterance are preserved where possible; at the same time the sentences are made more straightforward and therefore easier to read quickly. Supplementary information relating to background noises or effects not obvious to a viewer with a hearing impairment is also provided. The editor aims to convey sufficient information for the viewer to appreciate and enjoy the programme, without imposing an unreasonable reading load. Review of the programme tape with the script enables notes to be made regarding subtitle placement. It is helpful for the deaf viewer if subtitles are laterally positioned on the screen to match the position of the speaker. Further assistance is given in identifying a speaker by using differently coloured subtitles for different characters where possible. Notes can also be made on the script to indicate the time available for each segment, which will guide the later editing procedures. The editor prepares the subtitles using the keyboard and VDU display. Each subtitle is individually numbered and stored on the floppy disc. When all the subtitles have been entered for the complete programme, it is then necessary to enter the time-code which will specify when the subtitle is to be displayed, together with the time-code for cancelling the display. Thus two time-codes must be entered per subtitle. In an alternative method the processor calculates the necessary length of time for display of the subtitle, for a given reading rate, and automatically adds the appropriate ‘erase’ time-code. A print-out of the subtitle and associated time-codes can be produced. A typical print-out is shown in Figure 7.2. The programme would be pre-viewed on a colour monitor which would also have a display of the time-code generated by the time-code reader.

The method of subtitle preparation described allows for maximum flexibility. For example, a number of television programmes can be worked on concurrently, the subtitles being viewed independently of the teletext system, and in the order in which they will eventually be transmitted. If an amendment is needed to either the text or to the associated time-code, flexible editing facilites are available for corrections to be made. A floppy disc is a very convenient medium for storing a complete programme of subtitles with associated time-codes. However, floppy discs do impose restrictions on the editing arrangement since if any major editorial changes are made to the television programme, the complete disc has to be reprocessed. Furthermore, instant access to any part of the programme is not available to the editor.

Time-code Subtitle Text Colour Display Feature
00 11 05 02
3*
Anne, sorry to call you at home. C  
00 11 06 24
4*
Can you arrange to meet me at
lunchtime?
C Up 1
0011 0912
2*
Yes, of course. Y Add
C011 11 19
2*
DOOR BELL > W/R Effect
00 11 14 001
3*
Hold on, someone is at the door.    
Time-code hours, minutes, seconds, frames Ihh, mm, ss, ff).
+ DispIay time,
Colour C = cyan, Y= yellow, R = red, W= white.
W/R = white text on red background etc.
Display feature Up 1 = subtitle moves up \ line.
Add = added to existing text (add-on).
Effect = off-screen effect;arrow indicates position.

Figure 7.2 Typical subtitle print-out

A RAM disc is used in the more recent designs of subtitle preparation systems, so that all the subtitles for the complete programme are instantly available. When a programme has been completely subtitled, the contents of the RAM disc are transferred to a floppy disc for archival or operational purposes.

Subtitling of live programmes

As previously mentioned, preparation of subtitles in advance for a prerecorded programme usually now takes some 10 – 15 times the programme duration. During an unscripted ‘live’ broadcast, the subtitles must be composed, entered and formatted as the programme proceeds and it is almost impossible to achieve the same presentation standards as can be achieved when subtitles are prepared in advance. The problem becomes one of trying to present the viewer with sufficent information quickly enough for it to be in context, and to present it in a form which is easy to comprehend. These tasks can cause serious problems for the editor, particularly during a rapid live presentation of unscripted material. However, in practice, few programmes are live and completely unscripted with no information available beforehand about what will be said or who is participating. Portions of live programmes are often prescripted, particularly coverages of major public events and parts of news bulletins. The subtitle preparation system normally contains a file of advanced information relating to the event to assist the editor. Such files are normally called ‘shortforms’ and are accessed by a simple code. A shortform may contain two- or three-word names or phrases that are expected to occur frequently in a programme. For example, in a sports programme the individual players’ names would be stored in full, but accessed by a number. Before transmission a list of such names and phrases would be produced as background knowledge and information likely to be required during the programme. Appropriate abbreviations are chosen by the editor and stored with the full names as a dictionary in the subtitle preparation system. When a shortform is later required as part of the text of a subtitle, the processor automatically substitutes the longform from the stored directory in response to the simple code entered by the editor.

To further assist in subtitling it is common practice that two or three keyboards are able to access the processor simultaneously so that two or three editors can be involved at once. This technique is particularly valuable on sports type programmes as one editor can follow the play while the second editor can provide backup information or undertake subtitle preparation, as appropriate. An additional display monitor may be incorporated into the system so that shortform or other prepared notes can be made available to the editors without complicating the VDU display.

The use of a machine shorthand keyboard in conjunction with a specially trained operator can provide a faster input with certain languages. Phonetic codes representing speech are entered and these are decoded by the keyboard computer to produce a conversational transcription. Opinion is varied as to the value of such systems as they can produce ambiguous words or sentences under certain conditions; but the advantage of machine shorthand input is that a rate of about 100 words per minute can be sustained relatively easily.

Subtitle transmission

A subtitle page cannot simply be inserted according to the page number in the teletext magazine. If this were done, the page would be transmitted anywhere between 0 and 25 seconds after insertion (assuming a 100-page magazine using two television lines). Even inserting the subtitle at the end of the current page is inadequate, since the transmission delay would then vary between 0 and 0.25 seconds. It is therefore necessary to start transmitting the data for the subtitle on the first available data line after the cueing point. Special techniques must be used in the teletext system to give priority to the subtitle input and thus to allow the page to be inserted into the magazine in this manner.

Transmission of subtitles as part of a teletext magazine also places major limitations on television networks, particularly where the programme material on regional sections differs from that on the main network. Furthermore, regional stations often transmit network films (or other material) at times different from the main network. Consequentially, a programme on the main network will have subtitles at the wrong times for regional transmission. It is therefore necessary to intercept the subtitle pages at the regional station and to record them for transmission at the later time, with appropriate programme material. The equipment necessary for this purpose is shown in Figure 7.3. It is an extension of equipment required at a regional station for page exchange purposes (Chapter 6, page 70).

Referring to Figure 7.3, on record, the VCR is fed with the programme video signal and the teletext subtitle page only. The processor is programmed to output only the subtitle page, which is also line-shifted to occupy the last FBI line before the video signal. This is to prevent the VCR erasing the teletext data from the FBI. The data is inserted at full amplitude to help overcome limitations arising from shortcomings in the VCR’s frequency response.

On replay the teletext subtitle signal is decoded, then applied as an RS232 feed direct to the teletext system subtitle input port. The system software is programmed to give priority to the subtitle input port so that each subtitle is inserted into the magazine on the next available FBI line.

An alternative arrangement that avoids many of these complications is to devote a separate FBI line to the teietext subtitles. The subtitles can then be transmitted completely independently of the main teletext service. A further advantage of a separate FBI line is that regional stations, or other users, may use the subtitle information in the FBI with the video signal, independently of the teletext service. This is particularly important when the regional station is tape recording the video signal for transmission at a different time.

The use of a separate FBI line allows the programme to be simply recorded with the subtitle. When the programme is transmitted the subtitle is generated directly from the tape recorder along with the video signal. The only additional data processing required is the regeneration of the teletext data to compensate for the shortcomings of the recorder, and possibly the shifting of the data onto the correct FBI line for transmission. This line-shifting facility is a normal feature of a teletext data regenerator.

The use of a separate FBI line also simplifies teletext networking since the subtitle FBI line can be treated as programme-related information and is never separated from the video signal. It also overcomes the problem of floppy discs which contain the subtitle information becoming separated from programme tapes, or even being associated with the wrong programme tape.

Figure 7.3 Subtitle recording system for regional teletext service

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