Security field (video capture card), a variety of DVR cards, so many engineers and consumers, especially those who just entered the line, have no choice but to buy a card is more convenient and more effective. Monitor, look at the soft and hard points of the video capture card and the application.
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Video capture card soft and hard
Now as long as you buy a DVR card, the owner usually asks which type of card you want - soft card or hard card? Here we will first introduce the difference between the soft card and the hard card.
First, soft compression DVR
DVR with soft card is generally called soft compression DVR. It is actually a video capture card. It is equipped with monitoring software to realize video surveillance, video recording, playback history video and remote monitoring. Its hardware is one or more video capture chips. (eg: fusion878a, saa7130/7134, tw6802B/6805, etc.) Receive signals from analog cameras, convert them to digital signals, and then enter the motherboard directly from the PCI gold finger through the PCI bridge chip. The original digital video signal is executed in the memory. The CPU instructs the operation to compress and process the video and then store it on the hard disk. In addition, the original video data is also sent directly to the graphics card, previewed through the display.
The circuit board of the soft card is very simple. There is no compression chip and temporary memory chip on the board. The cost is low, generally about 1/3 of the hard compression, so the price is its biggest advantage. In addition, we can see from the principle that the soft compression DVR There is CPU compression, so its compression quality is good, video clarity is high, in the case of sufficient CPU resources, soft compression DVR in the video, network and other functions is no less than hard compression DVR.
Second, hard compression DVR
Hard compression DVR, also known as video capture compression card, is basically the same as soft compression principle. The difference is that after analog video is converted to digital signal, it is not directly sent to the motherboard, graphics card, memory through PCI, but by hard compression first. The DSP of the DVR card replaces the computer CPU to execute the compression algorithm instruction, compresses the memory chip on the DVR card, and then enters the motherboard through the PCI gold finger. Therefore, the hard-compressed DVR board has more DSP or other compression chips and memory chips. Therefore, the main advantages of hard-compressed DVR are mainly reflected in the large-channel monitoring, such as 32-channel full-time real-time surveillance video, soft compression is difficult to achieve, this market gap can be occupied by hard compression.
Video capture card technology application
Electronic devices have entered the daily life of people from obscurity. Faced with the ever-changing monitoring products in the market and the constantly updated monitoring card prices, people are always confused, so we only have to constantly understand the monitoring market and monitor Technology can be invincible.
With the continuous development of information technology, computer technology has been introduced into the field of video capture and video processing. The use of computers to process video information and digitally transmit video data has been widely used in many fields, and has been widely used in our aircraft flight test. There are many methods for video image acquisition, which can be divided into two categories: digital signal acquisition and analog signal acquisition.
Image acquisition chipset is used to complete image acquisition, frame memory address generation and image data refresh; in addition to setting the acquisition mode, the main processor does not participate in the acquisition process, we only need to take the collected at the corresponding frame memory address. Video data can 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 universal video A/D converter to achieve image acquisition. It is characterized by the fact that data acquisition takes up CPU time, requires high speed, low cost and is easy to implement, and can meet the needs of some image acquisition systems.
This system requires a maximum of 25 frames per second (set to be adjustable), the client displays up to 25 frames in real time (set to adjustable), saves to MPEG4 format, the screen requires a maximum resolution of 1024X768. Multi-channel video real-time acquisition uses VisionRGB-PRO card (Datapath, UK). This card can simultaneously collect two channels of video data in real time, basically meeting the requirements of this system, and then using a VGA matrix switcher to front-end data source. Four channels of video data are manually switched.
Hardware environment construction
The acquisition system mainly realizes the artificial switching real-time acquisition of the front-end four-way video data, and can simultaneously collect and store two video data at the server end (only one video capture card is used here), or can collect only one video data at a time. Then, the network transmits the video to the client in real time, and the server also displays the captured video in real time. In the video switching, the server can be switched on the server side or the client side. On the server side, the VGA matrix switch can be operated through the serial port to switch the corresponding video input and output ports, and the client can pass the network-server program corresponding module-string Line port - VGA matrix switching to switch the corresponding video input and output ports.
The large amount of video data requires the video data processing system to have real-time acquisition, large-capacity storage and real-time processing. The software needs to realize real-time acquisition of video data (up to two channels), control video interface, store and save video data in real time and send it to multiple clients. The implementation on the server side is the key to the whole system, and it also undertakes a lot of work here, so the requirements for software and hardware are also high. The above is the main function to be implemented on the server.
In the collection aspect, the most important thing is to have real-time performance. In this case, the data is acquired from the port in an event-driven manner, and the video data stream is collected and saved in the desktop display. The data collected by the video is to be processed by the corresponding module of the software. Set as a bitmap type video frame to facilitate display and encoding preservation on the server side. Divx encoding is used here, and Divx encoding is used to form a frame-based MPEG4 stream.
Server-side implementation
Divx decoding is also decompressed in a frame format, so it is advantageous to send a video stream in units of frames when transmitting data to the client. The media stream is divided into four streams: video stream, audio stream, text stream, MIDI stream. The video card is used to collect two video streams. When saving, each video stream is added with a text stream. The text stream is mainly added by the customer. The server time and some artificial input text information, there are generally two recording methods when recording two media streams, here is the way to record the video stream and text stream into a file, which is beneficial to the future of the file. Save and view. In the acquisition software implementation, the corresponding SDK (Software Development Kit) and API (application programming interface) are mainly applied, and VFW (Video for Windows) is also available. However, the latter method can realize a simple single-channel video capture card, and the first method for multi-channel video acquisition is more flexible, but the implementation is more complicated than the second one.
Coordination work on all aspects of the server is the key. The program starts by 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, wait. If you want to adjust the video capture card channel, you can use the serial port. The VGA matrix switcher sends corresponding commands to allow the VGA matrix switcher to switch between the corresponding input and output channels. It can also be switched between the client and the server through the network to the server serial port to the VGA matrix switcher for the corresponding input and output channels of the VGA matrix switcher (introduced when the client is introduced later). The original video file will be automatically saved after each switch. If there is video data after switching, a new video file will be automatically regenerated.
The use of LAN to transmit video data in real time has been widely used in some fields. The LAN is mostly wired LAN. Because the wired LAN technology is mature and the transmission speed is fast, when the large amount of video data is transmitted for a long time, the transmission rate is unstable and data jam is caused. The quality of the video transmission will be greatly reduced, which may cause ghosting, jitter, blooming, delay, and the like of the picture. The screen displayed on the server desktop is not encoded, but the network data transmitted and saved is Divx encoded, which effectively reduces the burden between the network transmission and the server.
In order to effectively and high-quality real-time transmission media streams on the local area network, various technologies are required, including network transmission layer protocol selection, coding (decoding) code technology, network transmission layer quality control technology, and the like.
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