Understand the main functions of video capture cards and their identification techniques

The purpose of purchasing a capture card is nothing more than to enable more convenient and effective monitoring. In the security field (video capture card), there are a variety of DVR cards, which makes many engineers and consumers, especially those who are new to the industry, at a loss as to where to start. You should pay attention to several major areas.

Main functions and technologies of video capture cards

Interface: There are several types of video capture card interfaces on the market. The interfaces of video capture cards include the interface between video and PC and the interface with analog video devices. Currently, PC video capture cards usually use a 32-bit PCI bus interface, which is inserted into the expansion slot of the PC motherboard to achieve communication and data transmission between the capture card and the PC. The capture card must have at least one composite video interface (VideoIn) to connect to analog video devices. High-performance capture cards generally have a composite video interface and an S-Video interface. General capture cards support both PAL and NTSC television formats.

It should be noted that video capture cards generally do not have TV antenna interfaces and audio input interfaces. Video capture cards cannot be used to directly capture TV RF signals, nor can they directly capture audio signals in analog videos. To capture audio, a sound card must be installed on the PC. The video capture card obtains digital audio through the sound card on the PC and synchronizes the audio with the captured digital video.

Function: What are the main functions of a video capture card? On a PC, a video capture card can receive analog video signals from the video input terminal, capture the signal, quantize it into a digital signal, and then compress and encode it into a digital video sequence. Most video capture cards have the function of hardware compression. When capturing video signals, they first compress the video signals on the card, and then transmit the compressed video data to the host through the PCI interface. General PC video capture cards use intra-frame compression algorithms to store digitized videos into AVI files. Some high-end video capture cards can also directly compress the captured digital video data into MPEG-1 format files in real time.

Since the analog video input can provide an uninterrupted source of information, the video capture card needs to capture each frame of the analog video sequence and transfer the data to the PC system before capturing the next frame. Therefore, the key to achieving real-time acquisition is the processing time required for each frame. If the processing time of each frame of video image exceeds the interval between two adjacent frames, data loss will occur, that is, frame loss. The acquisition card compresses the acquired video sequence first and then stores it in the hard disk. In other words, the acquisition and compression of the video sequence are completed together, eliminating the inconvenience of re-compression processing. Different grades of acquisition cards have different quality acquisition compression performance.

Driver and application: Some video capture cards need to be driven before they can be used normally. Video capture cards are generally equipped with hardware drivers to enable PC to control the capture card and data communication. Different capture cards have different drivers according to the operating system environment required. Only after the capture card is inserted into the expansion slot of the PC motherboard and the driver is correctly installed can it work normally. Capture cards are generally equipped with capture applications to control and operate the capture process. There are also some general capture programs, and digital video editing software such as Adobe Premiere also has capture functions, but these application software must be used in conjunction with the capture card hardware. That is, it can only be used after the capture card hardware is properly installed and driven.

Application of video capture card

Electronic equipment has gone from obscurity to enter people's daily lives. Faced with the ever-changing monitoring products on the market and the constantly updated monitoring card quotations, people are always confused. Therefore, we can only remain invincible if we continue to understand the monitoring market and monitoring technology.

With the continuous development of information technology, computer technology has been introduced into the field of video acquisition and video processing. Computer processing of video information and digital transmission of video data have been widely used in many fields, and have also been widely used in our aircraft test flights. There are many methods for video image acquisition, which can be basically divided into two categories: digital signal acquisition and analog signal acquisition.

The image acquisition chipset is used to complete the image acquisition, frame memory address generation and image data refresh; except for setting the acquisition mode, the main processor does not participate in the acquisition process. We only need to take out the acquired video data at the corresponding frame memory address to get the corresponding video data. This method has been significantly improved in terms of function, performance, reliability, speed, etc., but the cost is high. The latter uses a general video A/D converter to realize image acquisition. Its characteristics are that data acquisition takes up CPU time, has high requirements on processor speed, is low in cost, easy to implement, and can meet the needs of some image acquisition systems.

This system requires a maximum of 25 frames per second (adjustable), and the client displays a maximum of 25 frames in real time (adjustable), and saves in MPEG4 format. The maximum resolution is 1024X768. The multi-channel video real-time acquisition uses a VisionRGB-PRO card (Datapath, UK). This card can simultaneously acquire two channels of video data in real time, which basically meets the requirements of this system. A VGA matrix switcher is used to manually switch and acquire the four channels of video data from the front-end data source.

Construction of hardware environment

This acquisition system mainly realizes the real-time acquisition of four-channel video data at the front end by artificial switching. On the server side, two channels of video data can be acquired and stored at the same time (only one video acquisition card is used here), or only one channel of video data can be acquired at a time, and then transmitted to the client side for display via the network in real time. The server side also displays the acquired video in real time. In terms of video switching, it can be switched automatically on the server side or the client side. On the server side, the corresponding video input and output ports can be switched by operating the VGA matrix switch through the serial port. On the client side, the corresponding video input and output ports can be switched through the network-the corresponding module of the server program-the serial port-the VGA matrix switch.

The amount of video data is large, which requires the video data processing system to have the characteristics of real-time acquisition, large-capacity storage and real-time processing. The software must realize the real-time acquisition of video data (up to two channels), control the video interface, and save and send the video data to multiple clients in real time. The implementation on the server side is the key to the entire system, and it also undertakes a lot of work, so it is inevitable that the requirements for software and hardware are also high. The above are the main functions to be implemented on the server.

The most important thing in terms of acquisition is real-time performance. Here, data is obtained from the port in an event-driven manner. The acquired video data stream is encoded and saved while being displayed on the desktop. The acquired video data must be set as a bitmap video frame by the corresponding module of the software to facilitate display and encoding and saving on the server side. Divx encoding is used here, and Divx encoding forms an MPEG4 stream in frame format.

Server-side implementation

Divx decoding also decompresses in the format of frames, so it is beneficial to send video data streams in frames when sending data to the client. The media stream is divided into four streams: video stream, audio stream, text stream, and MIDI stream. The video card captures two video streams. When saving, each video stream is added with a text stream. The text stream mainly adds server time and some manually input text information at the request of the customer. There are generally two recording methods when recording two media streams. Here, the video stream and text stream are recorded in one file, which is conducive to the subsequent storage and reference of the file. In terms of acquisition software implementation, the corresponding SDK (Software development kit) and API (Application Programming Interface) are mainly used, and VFW (Video for Windows) can also be used. However, the latter method can be implemented with a simple single-channel video capture card. The first method is more flexible for multi-channel video acquisition, but the implementation is much more complicated than the second method.

Coordination of all aspects on the server side is the key. When the program starts, it will default to the last set video capture card channel. If there is video data, it will be displayed and saved. If there is no video data, it will wait. If you want to adjust the video capture card channel, you can use the serial port to send the corresponding command to the VGA matrix switcher to let the VGA matrix switcher switch the corresponding input and output channels. You can also use the client to connect to the server serial port through the network to the VGA matrix switcher to switch the corresponding input and output channels of the VGA matrix switcher (introduced later when introducing the client). The original video file will be automatically saved after each switch. If there is video data after the switch, a new video file will be automatically regenerated.

Real-time transmission of video data over LAN has been widely used in some fields. LANs are mostly wired LANs because of their mature technology and fast transmission speed. However, long-term transmission of large amounts of video data will also cause unstable transmission rates, data congestion, and a significant decrease in the quality of video transmission, which can easily cause ghosting, jitter, screen distortion, delay, etc. The images displayed on the server desktop are not encoded, but the video data transmitted and saved over the network is encoded by Divx, which effectively reduces the burden on network transmission and servers.

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In order to effectively and efficiently transmit high-quality real-time media streams on a local area network, the support of multiple technologies is required, including the selection of network transport layer protocols, encoding (decoding) technology, network transport layer quality control technology, etc.

Identify surveillance video capture cards

In the security field (video capture card), there are a variety of DVR cards, which makes many engineers and consumers, especially those who are new to the industry, at a loss. The purpose of purchasing a capture card is nothing more than more convenient and effective monitoring. You should pay attention to several major areas: whether soft compression or hard compression is better, what kind of card has the best image quality, whether it can realize remote functions, whether it is convenient to back up, how is the after-sales service, etc. Below we will distinguish and understand the advantages and disadvantages of various DVR cards, as well as introduce the relevant knowledge of purchasing capture cards one by one.

Soft and hard compression

Nowadays, whenever you buy a DVR card, the store owner will usually ask you what type of card you want - soft card or hard card? Here we will first introduce the differences between soft cards and hard cards.

1. Soft Compression DVR

We generally call the DVR with soft card as soft compression DVR, which is actually a video capture card. The card is equipped with monitoring software to realize functions such as video monitoring, recording, playback of historical videos and remote monitoring. Its hardware is one or more video capture chips (such as: fusion878a, saa7130/7134, tw6802B/6805, etc.) to receive the signal from the analog camera, convert it into a digital signal, and then enter the motherboard directly or through the PCI bridge chip from the PCI gold finger. The original digital video signal executes CPU instruction calculation in the memory, compresses and processes the video, and then stores it on the hard disk. In addition, the original video data is also sent directly to the graphics card and previewed through the monitor.

The circuit board of the soft card is very simple. There is no compression chip and temporary storage chip on the board. The cost is low, generally about 1/3 of the hard compression, so price is its biggest advantage. In addition, from the principle we can see that the soft compression DVR is compressed by the CPU, so its compression quality is better and the video clarity is high. When the CPU resources are sufficient, the soft compression DVR is no less than the hard compression DVR in terms of recording, network and other functions.

2. Hardware Compression DVR

Hard compression DVR, also known as video capture compression card, is basically the same as soft compression principle, but the difference is that after the analog video is converted into digital signal, it is not directly sent to the motherboard, graphics card, memory through PCI, but the DSP of the hard compression DVR card replaces the computer CPU to execute the compression algorithm instruction, and the memory chip on the DVR card is compressed, and then enters the motherboard through the PCI gold finger. Therefore, the hard compression DVR circuit board has more DSP or other compression chips and memory chips. Therefore, the main advantage of hard compression DVR is mainly reflected in large-number monitoring, such as more than 32 channels of full real-time monitoring video, which is difficult to achieve with soft compression, and this market gap can be occupied by hard compression.

Conclusion

From the above principles, we can see that the advantages of hard compression are:

1. Video compression is completed through built-in DSP, without occupying computer CPU resources;

2. Compressing before entering the PCI bus can save PCI bus bandwidth. However, due to the rapid increase in CPU cost performance, very cheap CPUs can easily compress 16-channel CIF video, resulting in the gradual degradation of the hard card advantage 1. In addition, with the emergence of PCI-E on the motherboard, the advantage of hard compression in saving PCI bandwidth is also weakening and eventually losing its meaning. Its main disadvantage is that the DSP chip on the card makes it very expensive;

3. The digital video is first compressed on the DVR card, and then decompressed and handed over to the graphics card monitor for preview display. In fact, everyone does not know that this process will cause the video signal to be damaged and the image quality will be reduced.

Note: The semi-soft and semi-hard cards that are often heard in the market do not exist at all, and there is no such saying. Friends must pay attention to this. This was mainly in 2002-2004. Because the CPU processing performance was limited and the price was expensive, the soft card could only meet 4-8 channels of real-time monitoring recording, while domestic monitoring full real-time 8-32 channels monitoring had a strong demand and market in government projects. At this time, hard compression achieved high-channel real-time monitoring by adding DSP and memory chips to the soft compression DVR card, and was widely used. In addition, at that time, there were almost no genuine soft compression DVRs in the domestic DVR market, most of them were pirated, and government projects generally did not use illegal pirated products. At that time, the hard compression DVR industry was booming and rapid. In 2004, a well-known domestic hard compression company once claimed in the media that soft compression DVR had entered the countdown to eliminate rogues. After 3 years, soft compression DVR not only did not die, but was gradually developing and growing, and the total sales volume has surpassed hard compression DVR. Especially in the field of civilian monitoring, where market competition relies on cost-effectiveness, soft compression is at a clear advantage? Later, in order to gain profits, dealers lied about semi-soft and semi-hard cards, but in fact they were generally soft compression cards.

Monitor image quality

The most important function of DVR is to play back historical videos. Playback quality is one of the most important performance indicators of DVR. The clarity and size of the image quality affect whether the management and monitoring personnel can find suspicious situations in time and clearly identify the suspects after a case occurs. Let's talk about several factors that affect image quality:

1. Chip

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Here we mainly talk about the soft card chip. The common chips for soft compression DVR cards on the market are FUSION878A, CX23811, CX25851 from CONEXANT of the United States, SAA7130, SAA7134 from PHILIPS and TW6800, TW6802, TW6802B, TW6805 from TECHWELL of the United States.

The American company CONEXANT is the earliest manufacturer of video capture card chips. Recently, it has developed the very competitive CX25835, which is an 8-in-1 chip with ultra-low power consumption, low heat generation, true color reproduction, no color cast, fine and clear image quality, and no outstanding price advantage. It may become the mainstream chip for DVR cards in the future. Currently, it has cooperated with domestic WAPA (wave particle) to develop a soft compression D1 8-in-1 card, which will be a historic turning point in the global DVR board industry. This chip was first made by Shenzhen Dongshun, but there has been no good software to match it and the price is very expensive, which is not accepted by the market. It also has no price advantage over similar products. In addition, the new 6802C from Zhonghengji has advantages over such cards in both image quality and price.

PHILIPS' SAA7130 chip has the advantages of 9-bit high-definition image quality, soft and warm image quality, and low noise. It has always been the mainstream chip for soft compression cards. Due to market reasons, 7130 was withdrawn from the market. There are also product chip limitations, and it was replaced by 7134. Currently, only one company in Shenzhen is investing in chips for the same product, and the effect is not as good as expected! The chips in the same industry are stronger than this chip in terms of compatibility and implementation, because the choice of chips is easier than before, so it is freer and unrestricted for manufacturers to make them; so SSA7134 will not become a mainstream product in the market at present;

Since 2003, TECHWELL has launched TW6802, 6800, 6802B, and 6805 chips for soft compression cards. The biggest advantage of this card is that it can switch acquisition without losing frames when used for non-real-time DVR, and its effect on audio and video synchronization acquisition is better than other chips. Currently, most of the audio and video synchronization acquisition cards in soft cards are this chip. This type of chip also solves the problem of full product compatibility, which is why this type of chip can become mainstream. Some people say that compatibility is a software problem, and some people say it is a hardware problem. In the end, there is no clear statement, but practice can explain everything. At present, the card with the best compatibility in the market is only this chip;

To sum up, the image quality of DVR is directly related to the chip of capture card, but the quality of first-class capture card also depends on DVR software, DVR circuit board design, and especially monitoring software. No matter how good the chip is, if it is not matched with mature monitoring software, its quality will be average.

As major chip manufacturers not only enter the field of security, their investment is also constantly increasing, and the chip processing and image clarity capabilities are becoming more and more excellent. In the past, one chip was used to process one channel, but now one chip is used to process four or eight channels, which is more prominent in terms of effect and image quality, including more advantages in chip processing, less busy lines in terms of speed and compression, and also reduces the hardware cost, and can get better quality assurance and stability, which is also a sign of behavioral progress; people who have used acquisition cards know that the maintenance rate of multiple chips is much higher than that of single chips; in this area, Zhonghengji Security found that the ratio is 7% and 1% based on market research. It is also a mainstream development of a product, which can reduce after-sales maintenance and reduce costs! In this area, Zhongliheng Security is a relatively complete company, and it is the first to propose a five-year warranty for video acquisition cards. It is conceivable that they are very confident in product quality and confidence, and at the same time, they also have the direct support of chip manufacturers and are inseparable from the R&D team.

2. Algorithm

In the domestic DVR industry, commonly used algorithms include H.264, MPEG-4, wavelet algorithm, MJPEG, etc. However, now according to the requirements of the project and various considerations, compression rate, image clarity, video space occupied, etc., in order to achieve a balance point, H.264 is adopted.

3. Code Stream

The bitrate is simply the amount of image data. The more data stored per second, the clearer the image. Reducing the bitrate means discarding some details in the image, which means less image data and less space, but the image will be less clear. The bitrate and image are also in direct proportion. Therefore, controlling the bitrate is also an important factor affecting image quality.

4. Resolution

Resolution, as the name implies, is the clarity of seeing an object. There are two things we need to pay attention to: display resolution and video resolution. Display resolution is the resolution of the monitor you are watching. Although the resolution of the monitor can now reach 1280*1024, most manufacturers' software does not support 1280*1024 high-definition resolution. It just forces the image to be squeezed or stretched up and down, making the image look deformed and the effect is not good. Currently, only one or two soft card software in the market can achieve high definition. Video resolution mainly affects the quality of the image and is determined by the algorithm. Just remember that the video resolution is proportional to the video capacity and image clarity. Now almost all manufacturers record more than 230M per hour in CIF format. As far as I know, Zhonghengji's Super Release III software is only 150M in CIF format (unlimited bit rate), and the D1 resolution video capacity is about 4 times that of CIF.

5. Several suggestions for obtaining clear images

First: Please try to buy ATI graphics cards, because the image quality of ATI graphics cards is recognized as the best in the industry. The graphics card industry is competing in rendering, line pipes, processing speed, 3D textures, etc. ATI graphics cards may not be as good as other manufacturers in some aspects, but in terms of image quality, vivid colors, delicateness, sharpness, and color reproduction, they are much better than other brands of graphics cards;

Second: Buy a good brand of monitor. The picture quality of the monitor mainly depends on the panel used by the monitor. Currently, monitors with good picture quality include PHILIPS, Samsung, ViewSonic, etc.

Third: Set the video resolution and bitrate high. As analyzed above, if the video resolution is high, the image will be clear. If the bitrate is high or unlimited, the image will be clear. In addition, the bitrate of the PTZ is mentioned here. Because the PTZ is always rotating, the picture changes a lot, and the data volume is very large. The more the picture changes, the larger the data volume. Under the same parameter settings (that is, the compression rate of all channels is the same), the video file of the channel with the PTZ will be larger than that of other channels. This is normal. If the video bitrate of this channel is forcibly limited, the video playback will be blurry and unclear. Therefore, it is not recommended to limit the bitrate of the PTZ.