In modern multimedia conference rooms, in order to meet the needs of different presentation occasions, there are usually multiple audio and video signal sources and display terminals, although these audio and video signal sources and display terminals may also have composite video (Composite-Video). , Super video (S-Video), component video (Component-Video), and even digital video (DVI, SDI) interfaces, but currently used in multimedia video conferences are composite video matrix, the main reasons are as follows aspect:

 

Composite video has good stability, compatibility and versatility, small transmission bandwidth and long transmission distance. However, chrominance and brightness share a frequency bandwidth of 4.2MHz (NTSC) or 5.0 ~ 5.5MHz (PAL), and there is relatively large crosstalk between each other. The requirements for equipment and transmission cables are not high. The signal source is rich and embedded. Cable investment is low.

 

Although S-Video is significantly better than composite video in reducing brightness loss and brightness crosstalk, it does not make a very obvious difference to common LCD projectors and DLP projectors, and the investment in embedded cables It is twice as much as composite video, so it is not widely used in engineering long-distance transmission.

 

Component video is significantly higher than composite video or super video at the level of signal format, but currently most of the meeting rooms are for computer display (VGA or RGBHV signal format) services, and require high equipment and transmission cables (depending on (Expected design standards and investment budgets), the investment in embedded cables is high.

 

Component video signals similar to Y, RY, BY, Y, Cr, and Cb are currently mainly used in the broadcasting industry, and will gradually transition to SDI or HD-SDI digital signal formats. Due to signal source and capital budget restrictions, conference room use not much. Due to the limitation of effective transmission distance (about 5 meters), DVI signals have not been widely used.

 

    To sum up, it is customary that the audio and video matrix defaults to the composite video format without special mention. The main equipments output in composite video format are: cameras, physical booths, cable TV demodulators, remote video conferences, video tape recorders, DVD players, etc. The audio and video matrix is ​​between the video source and the display or multiplexing terminal in the system. At the same time, it is responsible for the centralized control of different audio and video signal sources according to users' wishes.

 

    According to the different input and output channels, common video matrices are generally 8 × 2, 8 × 4, 8 × 8, 16 × 4, 16 × 8, 16 × 16, 32 × 8, 32 × 16, 32 × 32, 64 × 16, 64 × 32, 64 × 64, 128 × 128, etc. The conventional understanding is that the number before the multiplication sign represents the number of input channels, and the number after the multiplication sign represents the number of output channels. Regardless of the number of input and output channels of the matrix, their control methods are roughly the same: front panel key control, separate keyboard control, third-party control (RS-232 / 422/485, etc.), and can achieve the following functions:

 

    1) The same or different video source content can be displayed on different display terminals at the same time according to the needs of use

 

    2) Can handle and call various video signals such as camera, video player, video recorder, cable TV, video conference, etc. conveniently and quickly

 

    3) The administrator can independently monitor any video signal, but it will not affect the content and effect displayed by other terminals.

 

    4) The administrator can record any video signal, but it will not affect the content and effect displayed by other terminals

 

    5) The administrator can send any video signal to the conference terminal or other branch venues, but it will not affect the display content and effect of other ports.

 

    Like the BGBHV matrix, the basic principle of designing a video matrix is ​​to determine the number of channels of the matrix based on the number of signal sources and the number of display terminals. Due to the difference in matrix specifications (the number of channels), the price is very obvious, and the budget Under certain circumstances, the selection of the channel number of a matrix will become more sensitive, which is also a test for future expansion. In addition, several issues described below are also factors that need to be considered as the equipment selection.

 

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