1. The role of audio and video matrix

Modern multimedia conference rooms typically have multiple audio and video signal sources and display terminals to meet the needs of different presentation scenarios. Although these audio and video signal sources and display terminals may also have interfaces for Composite Video, S-Video, Component Video, and even Digital Video (DVI, SDI), the composite video matrix is still commonly used in multimedia video conferences, mainly due to the following reasons:

Composite videos have good stability, compatibility, and versatility, with small transmission bandwidth and long transmission distance. However, the chromaticity and brightness share a frequency bandwidth of 4.2MHz (NTSC) or 5.0-5.5MHz (PAL), resulting in significant crosstalk between them. The requirements for equipment and transmission cables are not high, the signal source is abundant, and the investment in embedded cables is relatively low.

Although S-Video is significantly better than composite video in reducing brightness loss and brightness/chromaticity crosstalk, it does not have a very significant difference compared to commonly used LCD projectors and DLP projectors, and the investment in embedded cables is twice that of composite video. Therefore, it has not been widely used in long-distance transmission in engineering.

Component videos have significantly higher signal formats than composite videos or super videos, but currently most of them serve computer displays (VGA or RGBHV signal formats) in conference rooms, with high requirements for equipment and transmission cables (depending on expected design standards and investment estimates), and high investment in embedded cables.

In summary, it is customary for audio and video matrices to default to composite video format unless otherwise specified. The main equipment output in composite video format are: camera, physical booth, cable TV demodulator, remote video conference, tape recorder, DVD player, etc. The audio and video matrix is intermediate between the video source and the display or multiplexing terminal in the system, which is responsible for centralized regulation of different audio and video signal sources according to the wishes of users.

According to the different input and output channels, common video matrices generally include 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 in the matrix, their control methods are roughly the same: front panel button control, split keyboard control, third-party control (RS-232/422/485, etc.), and they can all achieve the following functions:

1) It is possible to simultaneously display the same or different video source content on different display terminals according to usage needs

2) It can conveniently and quickly process and call various video signals such as cameras, DVD players, video recorders, cable TV, and video conferences

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

4) Administrators can record any video signal without affecting the content and effect displayed on other terminals

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

The basic principle of designing a video matrix, like the BGBHV matrix, is also to determine the number of channels in the matrix based on the number of signal sources and display terminals. Due to differences in matrix specifications (number of channels), the price is very obvious. When the budget is fixed, selecting the number of channels in a matrix will also become more sensitive, which is also a test for future expansion.

Excerpt from: The Age of Projection