Computers in TV presentation 

13 June 2022


Cover of Television & Radio 1986

From Television and Radio 1986, published by the Independent Broadcasting Authority

Viewers who appreciate the originality of so much of Channel 4’s programming may not so readily recognise the technical innovation underlying the smooth transitions between those programmes: a computerised transmission system, custom-designed for the channel, that is the most sophisticated in Europe, if not the world.

Take a typical junction between programmes: as one programme ends, the picture fades to black. Up comes a caption and the announcer mentions next week’s edition of the series, this gives way to a trailer for another programme, then a pointer to the programme following after the break, then a commercial break, then the distinctive animated 4 logo, then a smooth mix through to the next programme.

All of these transitions — as in all the other programme junctions throughout the day — are operated automatically by a computer that cues up videotape machines, switches to them and cues up captions, all with split-second accuracy. All the instructions for an entire day’s operation have been entered into the computer by presentation staff in advance with the timing and source of every single programme caption, promotion trail and other event. During transmission, presentation and engineering staff monitor the output, and someone from Presentation can intervene instantly to override the computer if there is a problem — or can trigger a programme junction to begin if there is a live relay where timings cannot be determined precisely beforehand. Otherwise the only human intervention during a break is from the announcer whose relaxation belies the need to complete his or her piece within the 10 seconds or so allotted before the computer automatically cuts to the next programme.

With the rare freedom to plan a new channel afresh from the start, Channel 4 was eager to use the latest technology to support its on-air transmissions. But although there were some computerised systems in the US and Japan, the channel’s Chief Engineer, Ellis Griffiths, could find nothing that permitted the standard of sophisticated on-air presentation that British viewers take for granted. So the channel designed its own custom-built system of software and interfaces, linking a DEC computer to Sony 1″ videotape machines, a Cox vision mixer, an Aston III character generator and a Quantel digital library system (which stores stills as individual TV frames on computer discs).


A bank of machines

Two of the video tape machines cued automatically by the system. In the foreground the computer that controls them.


This Computer Aided Transmission System (CATS for short) allows a whole day’s programme schedule to be specified in the minutest detail, second by second: once a technician has loaded the correct videotape on the machine, the computer will operate it automatically and cue it up to a particular frame by reading off an electronic time-code on the tape. It will also perform a range of cuts, fades and mixes between pictures.

Each ITV company inserts its own commercials into the Channel 4 signal. To keep 15 ITV companies informed of the precise second at which they should opt out of the national service and run their commercials, Channel 4 relays its own private data distribution service, which is relayed piggyback like teletext, encoded onto a line at the top of each field of picture that emanates from the channel’s headquarters in Charlotte Street, London, providing a colour-coded menu of the next sequence of events, updated every second. Accompanying this information are electronic cues which ITV companies can use to trigger the machines transmitting their own TV ads.


A man sits at a control desk

Presentation Control during transmission.


This system allows presentation staff to deploy their professional skills more efficiently, planning all the details of a day’s transmission in advance, without the risk of human errors live on transmission — and yet allowing the flexibility to deal live with last-minute changes.



And now with three years’ successful on-air experience in Britain, Channel 4 is exporting its technology abroad as its agents, Connolly Systems, find considerable interest among overseas broadcasters for the software system.



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