HD-MAC

HD-MAC was a proposed broadcast television systems standard by the European Commission in 1986 (MAC standard), a part of Eureka 95 project. It is an early attempt by the EEC to provide High-definition television (HDTV) in Europe. It is a complex mix of analogue signal (Multiplexed Analogue Components), multiplexed with digital sound, and assistance data for decoding (DATV). The video signal (1250 (1152 visible) lines/50 fields per second in 16:9 aspect ratio) was encoded with a modified D2-MAC encoder.

HD-MAC could be decoded by standard D2-MAC receivers (SDTV), but in that mode only 625 (576) lines and certain artifacts were visible. To decode the signal in full resolution required a specific HD-MAC tuner.

The European Broadcasting Union video format description is as follows: width x height [scan type: i or p] / number of full frames per second

As an example, the 1280×720p/60 format provides sixty 1280x720 pixel progressively scanned pictures each second. Lines are transmitted in the natural sequence: 1, 2, 3, 4, and so on.

European standard definition broadcasts use 720×576i/25, meaning 25 720 pixels wide and 576 pixels high interlaced frames: odd lines (1, 3, 5 ...) are grouped to build the odd field, which is transmitted first, then it is followed by the even field containing lines 2, 4, 6... Thus, there are two fields in a frame, resulting in a field frequency of 25 × 2 = 50 Hz.

The visible part of the video signal provided by an HD-MAC receiver was 1152i/25, which exactly doubles the vertical resolution of standard definition. The amount of information is multplied by 4, considering the encoder started its operations from a 1440x1152i/25 sampling grid.

Work on HD-MAC specification started officially in May 1986. The purpose was to react against a Japanese proposal, supported by the US, which aimed to establish the NHK-designed system as a world standard. Besides preservation of the European electronic industry, there was also a need to produce a standard that would be compliant with the 50 Hz field frequency systems (used by a large majority of countries in the world). Truth be said, the precisely 60 Hz of the Japanese proposal was also worrying the US, as their NTSC M-based standard definition infrastructure used a practical frequency of 59.94 Hz. This apparently minor difference had the potential for a lot of trouble.

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