Video re-production
Overview
The process of television re-production involves video and audio process- ing as well as video formatting and drive for the particular video display unit. Figure 9.1 shows the major sections of the video section of a television receiver set. The video input may be from an analogue or digital source and the latter may be standard definition or high definition. The analogue video may take several formats:
● CVBS signal obtained from an analogue terrestrial tuner or directly from a SCART connection.
● Y and C from an S-video connection.
● Component video Y, Pr, Pb.
● RGB via VGA port.
These analogue video signals are first fed into the next chip which selects the video signal to processes it as determined by the viewer. Modern TV receivers are designed to receive direct audio/video (AV) input from exter- nal sources such as video recorders, camcorders, satellite receivers and dig- ital television decoders. They also provide direct AV signals to peripherals such as video recorders and MPEG decoding audio systems. There are several ways for connecting AV devices to each other including the SCART connector, video coupling (S-video, component video, RGB), digital video interface (DVI), HDMI, VGA for PC, universal serial bus (USB), RS232 and FireWire. Refer to Chapter 25 for details.
Video processing includes colour decoding using a comb filter which separates the luminance Y signal from the chrominance components. The resulting RGB signals are then fed into the next stage for video formatting.
The purpose of video formatting is to ensure that the incoming video which may be interlaced or progressive, and may have a variety of line and frame frequencies (PAL, NTSC, PC VGA) is converted into the native fixed format or resolution of the display unit. Formatting is followed by the drive circuitry which may be RGB amplifiers in the case of a cathode ray tube (CRT) display, scan and sustain drive in the case of a plasma panel or line (row) and data (column) drivers in the case of an LCD display.
Video formatting is not necessary if the display unit is a CRT. Cathode ray tubes do not have a fixed resolution in which case, analogue RGB is fed directly into the tube via a driver amplifier.
Digital video may be obtained from a standard definition terrestrial DVB decoder consisting of a digital terrestrial tuner, COFDM demodulator and
an MPEG-2 decoder. High-definition video would arrive as an uncompressed digitised video via HDMI port to an HDMI decoder or receiver which converts back into digitised R, G, B as illustrated in Figure 9.1. Both digital video signals are fed directly into the video formatting and drive section of the receiver.
Audio from a terrestrial analogue broadcast is tapped off the CVBS signal by a SAW filter and following demodulation by the sound detector, it is fed to a multi-media sound processor, amplified and fed into the speak- ers. For digital reception, stereo sound forms part of the transport stream produced by the COFDM demodulator. It is MPEG-2 decoded and fed to the sound select switch for further processing and amplification. External sound in the form of phono L/R connection may be fed directly to the sound select switch. However, audio may also be available in a digitised form via a coaxial or a fibre optic (SPDIF) connection in which case it is fed directly to the multi-media sound processor (MSP).