C-MAC/packet is a variant of the family of MAC (

Multiplexed Analogue Components Multiplexed Analogue Components (MAC) was an analog television standard where luminance and chrominance components were transmitted separately. This was an evolution from older color TV systems (such as PAL or SECAM) where there was interferen ...

) systems for

television broadcasting A television broadcaster or television network is a telecommunications network for the distribution of television content, where a central operation provides programming to many television stations, pay television providers or, in the United ...

, developed by IBA and approved by the

European Broadcasting Union The European Broadcasting Union (EBU; , UER) is an alliance of Public broadcasting, public service media organisations in countries within the European Broadcasting Area (EBA) or who are member states of the Council of Europe, members of the ...

(EBU) for satellite TV transmissions. It was an

analog television Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, instantaneous phase and frequency, ...

standard where

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...

and

chrominance Chrominance (''chroma'' or ''C'' for short) is the signal used in video systems to convey the color information of the picture (see YUV color model), separately from the accompanying Luma (video), luma signal (or Y' for short). Chrominance is usu ...

components are transmitted separately in time rather than separately in frequency. This was an evolution from older color TV systems (such as

PAL Phase Alternating Line (PAL) is a color encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...

SECAM SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''sequential colour memory''), is an analog color television system that was used in France, Russia and some other countries or territories of Europe and Africa. ...

) where there was interference between chrominance and luminance.

Technical details

C-MAC required a bandwidth of about 22 MHz, making it unsuitable for

direct-to-home Satellite television is a service that delivers television programming to viewers by relaying it from a communications satellite orbiting the Earth directly to the viewer's location.ITU Radio Regulations, Section IV. Radio Stations and Systems ...

cable Cable may refer to: Mechanical * Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof * Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...

broadcast. The transmitter switches between FM (vision) and PSK (sound/data) modulation during each television line period. The digital information is modulated using 2-4PSK (

phase-shift keying Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave. The modulation is accomplished by varying the sine and cosine inputs at a precise time. I ...

), a variation of quadrature PSK where only two of the phaser angles (±90°) are used, with a data rate of 20.25 Mbit/s. This allows for the transmission of up to eight high quality (15 kHz bandwidth) sound channels. C-MAC data was sent to the transmitter separately from the vision. The C-MAC standard included a standard scrambling system,

EuroCrypt EuroCrypt is a conditional access system for Multiplexed Analogue Components-encoded analogue satellite television Satellite television is a service that delivers television programming to viewers by relaying it from a communications satell ...

, a precursor to the standard

DVB-CSA The Common Scrambling Algorithm (CSA) is the encryption algorithm used in the Digital Video Broadcasting, DVB digital television broadcasting for encrypting video coding, video streams. CSA was specified by ETSI and adopted by the DVB consortium i ...

encryption system.

E-MAC

E-MAC (Extended MAC) is 16:9 version of C-MAC. Originally E-MAC was designed for 15:9 pictures, it later adopted the 16:9 aspect ratio. * In E-MAC all the 4:3 information is transmitted exactly as in C-MAC so that C-MAC receivers are still compatible. * E-MAC hides extra luminance and chrominance information in the field blanking interval and parts of the line blanking interval. * E-MAC has a lower data capacity because luminance is hidden where data would usually be located. * A 'steering' signal is transmitted to indicate to the 16:9 receiver whereabouts the 4:3 picture information. * E-MAC receivers stitch the 4:3 and helper widescreen data into a seamless 16:9 picture.

References

{{reflist Television technology Video formats

Technical details

E-MAC

See also

References