Video recorder scheduling code

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.

History

Before the advent of on-screen displays, the only interface available for programming a home video recorder was a small LED or LCD panel and a small number of buttons. Correctly recording a specific program was therefore a somewhat complex operation for many people; scores of jokes have referred over the years to the need to "have a 12-year-old" or someone technically adept to program successfully a home video recorder or to avoid having a perpetual blinking "12:00" on the recorder's display. G-Code, VideoPlus+ and ShowView were introduced to remove this difficulty, and even with modern user interfaces for manual setting, they still offer a more convenient means of specifying a program to record.

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.

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, New Zealand 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, because of TV programs' schedule are different, the coding has to be adjusted in each of the regions and recording equipment is not interchangeable.

Algorithms

The actual algorithms used to encode and decode the TV guide values from and to their time representations were published in 1992, but only for 6 digit codes or less. [1] ^[1]

Several open source code 6 digit examples are available [2], [3]. An implementation using Excel macros is also available [4].

One problem found during reverse engineering efforts is that the algorithm seemed to change for seven and eight digit codes.

Although not well known, source code that also works with 7 and 8 digit codes was posted anonymously in 2003. The code for the full 8 digits was written in C and later converted to Perl. [5]

References

^ K. Shirriff, C. Welch, A. Kinsman, Decoding a VCR Controller Code, Cryptologia, 16(3), July 1992, pp 227-234.

External links

[1] K. Shirriff, C. Welch, A. Kinsman, Decoding a VCR Controller Code, Cryptologia, 16(3), July 1992, pp 227-234.

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