Component Encoding
In the digital processing and transmission of color TV signals, a common method is to digital coding the three components (Y, R-Y, B-Y. This is the component encoding. In addition, full-signal encoding is used to directly encode all-television signals to form digital video signals. Generally, its sampling frequency is FS = 4fsc. In this way, the NTSC and palth signals are formed to facilitate the orthogonal sampling structure of Inter-line, inter-field, and inter-frame signals.
1. sampling frequency
When the bandwidth of Brightness Signal y is 5.8mhz ~ 6 MHz, two color difference signal (R-Y) and (B-Y) of the bandwidth is 2 MHz, can obtain satisfactory bandwidth.
2. International standards for TV studio component encoding: the sampling frequency of Y/(R-Y)/(B-Y) is
13.5 MHz/6.75 MHz // 6.75 MHz. Because the sampling frequency of the two chromatic aberration signals in this standard is 2/4 of the brightness signal, this standard is referred to as: 4: 2: 2. the sample points in each line of the two chromatic aberration signals are 1/2 of the Brightness Signal.
3. Digital Component Video signal interface
The digital signal of the component encoded according to: 4: 2: 2 sets the digital interface standard for parallel transmission. According to the standard, the 8-bit characters in each sample are transmitted in parallel in eight balanced wires. The three digital component signals constitute a time-division multiplexing code stream. The transfer order is:
CB, Y, Cr, Y, CB, Y, Cr, y .......
In order to enable reception and start synchronization, A 27mhz clock signal is sent in the ninth line.
4. SDI Signal
In the digital studio, the signals circulating between devices are serial digital interface signals (SDI). The serial digital component signals are converted from parallel, in 10-bit quantization, the digital transmission rate is 270 Mb/s. It is an Uncompressed Digital Video signal, which has high requirements on transmission bandwidth and transmission quality. The studio can meet such transmission conditions, so as to provide high-quality signals to meet the requirements for performances.
The SDI signal does not transmit the clock signal separately. The receiver must extract the clock information from the signal itself. To avoid too many connections between 0 and 1, the sender must encode the channel of the serial data in the scrambling mode. Because the SDI signal is transmitted with a reversed NRZ code, that is, the nriz code, therefore, a NRZ to nriz converter must be connected after the disturbing device.
5. ASI signal (asynchronous serial)
This is an increasingly used asi. The transmission media can be optical cables or cables. Fixed connection rate (270 Mb/s ).
The working process of this transmission mode is as follows: what the sender wants to send is a byte synchronization MPEG-2 transfer packet, first by 8 Bytes/10 bytes encoding, the transfer stream is adapted from 8 to 1 byte to 10 bytes, and then transmitted through a fixed 270 Mbit/s after String Conversion,
ASI transmits the encoded code stream of the MPEG-2 source.
The SDI (serial digital inter-face) signal defined by the SMPTE 259m standard is one of the digital video standards widely used in the current digital broadcast system, its biggest advantage is that it provides a large number of auxiliary data areas (an-cillary data space), which can be used to embed audio signals and other useful signals. Corresponding to the line and field invisibility period in the simulated video signal, some special time series reference signals (timing reference signa1) are defined in the digital video to achieve line-to-field synchronization, after the analog video signal is digitalized, the digital signal corresponding to the row and field hidden area in the Digital Video Stream does not actually carry valid video data, which is called the auxiliary data area. Package the serial digital audio that complies with the AEs/EBU standard in a certain format, and enter the packaged audio data in the auxiliary data area of the video data, you can embed the audio data into the video data stream. The auxiliary data area of the existing video format can accommodate up to 16 channels of audio data, which is sufficient to meet the actual needs of the vast majority of Digital Studios.
The audio embedding technology allows audio and video signals that must be separately transmitted in the past to be transmitted in a video cable, this greatly simplifies the hardware overhead and audio/video signal routing policies required for audio/video interconnection in the studio, and enables synchronous transmission and playback of audio and video.
The HD-SDI is an interface specification that is transmitted per SMPTE 292 m, at a signal rate of 1.485 Gbit/s or 1.485/1.001 Gbit/s. This specification specifies the data format, channel encoding method, signal specification of the coaxial cable interface, connector, cable type and optical fiber interface.
SDI is a serial digital interface (serial digital interface) technology that transmits baseband digital video signals that comply with SMPTE standards through a single cable.
Baseband Digital Video signals are usually processed as parallel signals in devices or devices. If direct transmission is performed, the Brightness Signal is 10 bits, the color signal is 10 bits, the clock signal is 1 bits, and the 1 bit synchronization signal is 22 Bits, that is, 22 parallel transmission channels are required. This is not only difficult to operate. In the case of parallel signals, it will also cause the phase difference between the signal data and the clock, and it is impossible to transmit long distances.
SDI can transmit all the brightness, color, synchronous, and clock information through a single cable, so it can be transmitted over long distances. However, high transmission rates are required. The premise of SDI signal is that there is no compressed baseband digital video signal. Unlike the mpeg signal formed after the baseband digital video signal is compressed, the SDI signal does not have any image quality reduction or delay caused by compression (at least 200 msec ). These are the reasons why the TV station chooses SDI. SD serial digital (SD-SDI) signals can transmit 350 meters through a coaxial cable 5cfb or 1189a, so you do not have to pay too much attention to the performance of the cable when creating the system. In the era of high definition serial digital (HD-SDI) signal, the transmission of this type of coaxial cable is difficult to reach M or above. If you need to transmit a longer distance, you need to choose a high foam media coaxial cable with lower attenuation. The strength of such cables is relatively low, so you need to pay attention to the cable deformation when bundling the cables, because the cable deformation will cause the error code. Even if this type of Low-attenuation coaxial cable is used, only HD Digital Signals of less than 180 meters can be transmitted, and sometimes degraded signals must be restored using relay devices. Therefore, in the establishment of a HD-SDI system, the construction of coaxial cable is simple, low cost and other factors. Ah ......
Therefore, the application scenario also depends on the economic basis. To put it bluntly, it is money.
