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With the improvement of the quality of life, people's viewing needs have also increased, 3D, 4K, HDR and other technologies have all appeared, and in terms of data transmission, the interface on the device is increasing, to meet the various needs of users. The more common ones in life are AV interface, DVI interface, HDMI interface, USB interface, etc., among which the HDMI interface is the most high-end.

The meaning of the HDMI interface

The HDMI interface is also called High Definition Multimedia Interface (HDMI), which is a digital video/audio interface technology. It is a dedicated digital interface suitable for image transmission, which can transmit audio and video signals simultaneously. There is no need to perform digital/analog or analog/digital conversion before signal transmission.

Simply put, the HDMI interface is an interface for transmitting video and audio signals. The content manufacturing device can transmit images and sounds to the viewing device with high efficiency through HDMI. Such interfaces are common in smart TVs, set-top boxes, projectors, etc., and their interfaces are inverted trapezoidal and relatively flat. As shown below:

Evolutionary history of HDMI

In fact, the technology that first appeared in the transmission field was DVI instead of DHMI. The appearance of DVI interface was widely used in the output field at that time, but with the development of digital high-definition video technology, DVI interface began to expose various problems. Even to a certain extent, it has become a bottleneck in the advancement of digital imaging technology. Therefore, whether it is IT vendors, flat-panel TV manufacturers, or many publishers in Hollywood, there is an urgent need for a better interface technology that can meet the future development of the HD video industry. It is for these reasons that the HDMI standard is promoted. The birth of.

HDMI 1.0

The earliest version of HDMI 1.0 was introduced in December 2002. Its biggest feature is the integration of the digital interface of the audio stream, which is more advanced and convenient than the popular DVI interface in the PC interface at the time. HDMI version 1.0 supports video streaming from DVD to Blu-ray format, and has CEC (consumer electronics control) function, which means that in the application, a common contact can be formed between all connected devices, and the device group can be more conveniently controlled. .

HDMI 1.1

May 2004, HDMI 1.1 version interview. Added support for DVD audio.

HDMI 1.2

The HDMI 1.2 version was launched in August 2005, which largely solved the problems of low resolution supported by HDMI 1.1 and poor compatibility with computer equipment. The 1.2 version of the pixel clock runs at 165MHz and the data volume reaches 4.95 Gbps, so 1080P can be achieved. It can be considered that the 1.2 version solves the problem of the 1080P of the TV and the point-to-point problem of the computer.

HDMI 1.3

In June 2006, the HDMI 1.3 update brought the biggest change to increase the single link bandwidth frequency to 340MHz, and also enabled these LCD TVs to obtain 10.2Gbps data transmission. The 1.3 version of the line has 4 pairs of transmission channels. One pair of channels is a clock channel, and the other three pairs are TMDS channels (minimizing the transmission differential signal), and their transmission speed is 3.4GBPS. Then 3 pairs of 3*3.4=10.2GPBS can greatly expand the 24-bit color depth supported by HDMI1.1 and 1.2 to 30, 36 and 48 bits (RGB or YCbCr). HDMI 1.3 supports 1080P; some less demanding 3D also supports (there is no theoretical support, actually some can).

HDMI 1.4

The HDMI 1.4 version already supports 4K, but is limited to a bandwidth of 10.2Gbps, which can only reach 3840×2160 resolution and 30FPS frame rate.

HDMI 2.0

HDMI 2.0's bandwidth is expanded to 18Gbps, support plug and play and hot swap, support 3840 × 2160 resolution and 50FPS, 60FPS frame rate. It also supports up to 32 channels in audio and up to 1536kHz sampling rate. HDMI 2.0 does not define new data lines and connectors, interfaces, so it can maintain perfect backward compatibility with HDMI 1.x, and existing Class 2 data lines can be used directly. HDMI 2.0 does not replace HDMI 1.x, but is based on the latter enhancements. Any device that wants to support HDMI 2.0 must first guarantee basic support for HDMI 1.x.

HDMI 2.0a

The change in HDMI 2.0a is not that big. Its main update is only one place, which is to add support for HDR format transmission, which can significantly enhance image quality.

HDMI 2.0b

HDMI2.0b is compatible with all HDMI pre-format versions, and is not much different from HDMI2.0a. HDMI2.0b is also the latest version of HDMI so far.

HDMI interface type

The HDMI interface is divided into A, B, C, and D types. Type A is the most common type. Generally, flat panel TV or video equipment provides interfaces of this size. Type A has 19 pins, width is 13.9 mm, thickness is 4.45 mm, and devices can be seen now. 99% are HDMI interfaces of this size.

Type B is very rare, with 29 stitches and a width of 21 mm. The transmission bandwidth is almost double that of Class A. It is completely "strong" in home applications and is now only used in some professional situations.

Class C is born for small devices. Its size is 10.42×2.4 mm, which is nearly 1/3 smaller than Type A. The application range is small, and it is mostly used in devices such as smartphones.

Type D is the latest interface type, and its size is further reduced. It adopts a double-row pin design and is similar in size to the miniUSB interface, making it suitable for portable and in-vehicle devices.

HDMI interface is different, but the function is the same, usually the quality of the HDMI interface, plug and play life will not be less than 5000 times, can be used for 10 years per day, it should be said that it is very durable. It is also worth mentioning that HDMI can be backward compatible with DVI interface. It can be connected to some older DVI devices through the commercially available HDMI-DVI adapter. Because DVI also uses TMDS mode, DVI devices will be found after the device is connected. Without CEC (consumerelectronics control) function, it can not accept audio signals, but it does not affect the transmission of video signals (it may need to be adjusted with grayscale), so some monitors with DVI only can also be connected to HDMI devices.

In addition to the different types, the HDMI interface also corresponds to different functions.

The first: HDCP 2.2, this technology protects high-value digital movies, TV shows and audio content from illegal theft and copying.

The second one: HDMI-ARC (Audio Return Channel) function, used for the output of TV digital audio, can be connected to the power amplifier that also supports ARC function, and the sound of the TV is transmitted to the power amplifier.

The third: bit refers to the color depth, the general notebook screen is 6bit, the high-end 8bit, the special professional 10bit, can be understood as the color depth of 2 to the 10th power, and 10bit specifically refers to a video encoding technology, can provide Very high video quality, able to show extraordinary detail in the gradual change and change of color, but the configuration requirements for playing 10bit is still very high.

Fourth: MHL technology delivers up to 4K Ultra HD uncompressed video with eight channels of digital audio using only five cables while charging mobile devices.

Finally, let's summarize the advantages of HDMI:

1. Quality: HDMI is a digital interface. Since all analog connections (such as component video or S-video) require no loss when converting from analog to digital, it provides the best video quality. This difference is especially noticeable at higher resolutions, such as 1080p. Digital video will be sharper than component video, eliminating the softness and smearing found in component video. Tiny, high-contrast details such as text take this difference to the limit.

2, ease of use: HDMI integrates video and multi-channel audio in a single cable, eliminating the cost, complexity and confusion of the multi-cable used in current A/V systems. This is especially useful when upgrading or adding devices.

3, high intelligence: HDMI supports two-way communication between video sources (such as DVD players) and DTV, enabling new features, such as automatic configuration and one-click playback. By using HDMI, the device automatically transmits the most efficient format for connected displays (eg 480p vs 720p, 16:9 vs 4:3), eliminating the need for consumers to scroll through all formatting options to guess the best viewing format.