HD-MAC was a proposed TV norm . It was an early attemp by the EEC to provide HDTV in Europe. Unlike DVB, HD-MAC was basically an analogue signal, multiplexed with digital sound, a complex mix of analogue and digital.
Video and audio were uncompressed, and required up to 36 mhz per transmission.
Video was broadcasted using a modified D2-MAC encoder. Standard resolution was 1250 (1152) lines/50 frames in 16:9 aspect ratio.
HD-MAC could be decoded by a standard D2-MAC receivers, but in that mode only 625 (576) lines and certain artefacts were visible. In order to decode the signal in full resolution, an specific HD-MAC tuner was needed.
In the 1992 Summer Olympics, an experimental HD-MAC broadcasting took place. 100 HD-MAC receivers (in that time, retroprojectors ) in Europe were used to test the capabilities of the standard. This project was financed by the EEC. The PAL-converted signal was used by regular broadcasters such as SWR, BR,BR,3Sat ... .
Today, the norm is regarded obsolete.
Technical details
The signal was captured with 50 full frames per second, each at a resolution of 2048×1152. In order to increase the horizontal resolution of the D2-MAC norm, only its bandwith had to be increased. This was easily done as unlike PAL, the sound is not sent on a subcarrier, but multiplexed with the picture. However, to increase the vertical bandwith was a bit more complicated, as the line frequency had to stay at 15'625 Hz, in order not to break compatibility with D2-MAC. This offered three choices:
- 50 frames per second with only 288 lines for fast moving scenes,
- 25 frames per second with 576 lines for normally moving scenes, or
- 12.5 frames per second with all 1152 lines for slow motion.
As none of the three modes would have been sufficient, the choice during encoding was not made for the whole picture, but for little blocks of 8×8 pixels. The signal then contained hints which deinterlacing method the decoder should use.
In order to fully decode the picture, the signal has to be digitized and then read from the memory several times.
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