Video recorder scheduling code

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For the CNC programming language, see G-code.

VCR Plus+, G-Code, VideoPlus+ and ShowView are different names for essentially the same system for programming video recorders. These names are all registered trademarks of Gemstar-TV Guide International, who developed these algorithms for use in integrated endecs.

1 History
2 Concept
3 Branding
4 Algorithms
5 External links

[edit] History

Before the advent of on-screen displays, the only interface available for programming a home video recorder was a small LCD panel and a small number of buttons. Correctly recording a specific program was therefore a somewhat complex operation, the difficulty of which has entered into folklore in many places. G-Code, VideoPlus+ and ShowView were introduced to remove this difficulty, and even with modern user interfaces for manual setting, still offer a more convenient means of specifying a program to record.

[edit] Concept

The central concept of the system is a unique number, a PlusCode, assigned to each program, and published in TV listings in newspapers and magazines. To record a program, the number is taken from the newspaper and typed into the video recorder, which will then record on the correct channel at the correct time. The number is generated by an algorithm from the date, time and channel of the programme, and so does not rely on anything being broadcast over the air. This means it will not compensate for a disrupted schedule due to live sporting events or news bulletins, but many video recorders with these systems also incorporate PDC and will use that to alter times if possible.

[edit] Branding

This system has been licensed to TV and VCR manufacturers in about 40 countries, but is known under different names. It is known as VCR Plus+ in the USA and Canada, G-Code in Japan,China and Australia, VideoPlus+ in Ireland and the UK and ShowView in the rest of Europe and also in South Africa. The system is called VideoPlus+/ShowView in Europe because Philips has a trademark registration for "VCR", and as G-Code ('G' for Gemstar) in Japan because VCR is not a common abbreviation there ('VTR' is used instead). However, the coding is different in each of the regions and recording equipment is not interchangeable.

[edit] Algorithms

The actual algorithms used to encode and decode the TV guide values from and to their time representations is not completely understood, although they have been partially reversed engineered, and several open source code examples are available [1], [2]. One problem found during reverse engineering efforts is that the algorithm seem to change for seven and eight digit codes, which are the currently undetermined encodings.