The purpose of purchasing a capture card is nothing more than more convenient and more effective monitoring, security field (video capture card), a variety of DVR card dazzling, so that many engineering companies and consumers, especially newcomers No way to start, you should pay attention to a few big areas.
Main functions and technologies of video capture card
Interface: The video capture card interfaces on the market can be divided into several types. The interface of the video capture card includes the interface between video and PC and the interface with analog video equipment. At present, the PC video capture card usually uses 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 with analog video equipment. High-performance capture cards generally have a composite video interface and an S-Video interface. General capture cards support both PAL and NTSC TV standards.
It should be noted that the video capture card generally does not have a TV antenna interface and audio input interface. The video capture card cannot be used to directly collect the TV RF signal, and the audio signal in the analog video cannot be directly collected. To collect sound, a sound card must be installed on the PC. The video capture card obtains the digital sound through the sound card on the PC and synchronizes the sound with the collected digital video.
Function: What are the main functions of the video capture card? On the PC, the video capture card can receive the analog video signal from the video input terminal, collect and quantize the signal 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 collecting video signals, the video signal is first compressed on the card, and then the compressed video data is transmitted to the host through the PCI interface. The general PC video capture card uses the intra-frame compression algorithm to store the digitized video as an AVI file. Some high-end video capture cards can also directly compress the collected digital video data into MPEG-1 format files in real time.
Because the analog video input can provide an uninterrupted source of information, the video capture card needs to capture each frame of the image in the analog video sequence, and transfer these data to the PC system before collecting the next frame of image. Therefore, the key to real-time acquisition is the processing time required for each frame. If the processing time of each frame of the video image exceeds the interval between two adjacent frames, data loss will occur, that is, frame loss. The capture card is to compress the acquired video sequence first, and then save it to the hard disk, which means that the acquisition and compression of the video sequence are completed together, eliminating the inconvenience of performing the compression process again. Different grades of capture cards have different quality capture compression performance.
Drivers and application programs: Some video capture cards need to be driven before they can be used normally. Video capture cards are generally equipped with hardware drivers to achieve PC control and data communication of the capture card. According to the operating system environment required by different capture cards, there are different drivers. Only after the acquisition card is inserted into the expansion slot of the motherboard of the PC and the driver is correctly installed can it work normally. The acquisition card is generally equipped with an acquisition application program to control and operate the acquisition process. There are also some general acquisition programs, digital video editing software such as Adobe Premiere, etc. also have acquisition functions, but these application software must be used in conjunction with the acquisition card hardware. That is, it can be used only after the hardware of the capture card is installed and driven normally.
Application of video capture card
Electronic equipment has entered the daily life of people from obscurity. In the face of the ever-changing surveillance products on the market and the constantly updated quotation of surveillance cards, people are always confused, so we only have to constantly understand the surveillance market and surveillance Technology is invincible.
With the continuous development of information technology, computer technology has been introduced into the fields of video acquisition and video processing. Processing video information with computers and transmitting video data with numbers have been widely used in many fields, and have also been widely used in our aircraft test flights. There are many methods of video image acquisition, which can be basically divided into 2 categories: digital signal acquisition and analog signal acquisition.
The image acquisition chip set is used to complete the 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 out the collected frame memory address The corresponding video data can be obtained from the 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-purpose video A / D converter to achieve image acquisition, which is characterized by the fact that data acquisition takes up CPU time, requires high processor speed, low cost, 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 as adjustable), the client displays a maximum of 25 frames in real time (set as adjustable), saved in MPEG4 format, and the screen resolution is 1024X768. Real-time multi-channel video acquisition uses VisionRGB-PRO card (UK Datapath company), this card can simultaneously capture two channels of video data in real time, basically meet the requirements of this system, and then use a VGA matrix switcher to the front-end data source Four channels of video data are collected by manual switching.
Construction of the hardware environment
This acquisition system mainly realizes artificially switched real-time acquisition of the front-end four-channel video data. On the server side, two channels of video data can be collected and stored at the same time (only one video capture card is used here), or only one channel of video data can be collected at a time And then transmitted to the client display in real time via the network, the server also displays the collected video in real time. In terms of video switching, the server or the client can switch on its own. On the server, the VGA matrix switch can be operated through the serial port to switch the corresponding video input and output ports. On the client, the network-server program corresponding module-serial can be used. Line port-VGA matrix switch to switch the corresponding video input and output ports.
The large amount of video data requires the video data processing system to have the characteristics of real-time acquisition, large-capacity storage and real-time processing. The software should realize the real-time collection of video data (up to two channels), control the video interface, and encode and save the video data in real time and send it to multiple clients. The implementation on the server side is the key to the entire system, and a lot of work is also undertaken here, so it is inevitable to have high requirements on software and hardware. The above are the main functions to be implemented on the server.
The most important thing in the collection is real-time. Here, the event-driven method is used to obtain data from the port. The collected video data stream is displayed on the desktop and then encoded and saved. The data collected by the video must be processed by the corresponding module of the software. Set the video frame as a bitmap format to facilitate display and encoding on the server side. Divx encoding is used here. After Divx encoding, an MPEG4 stream in frame format is formed.
Server-side implementation
Divx decoding is also decompressed in frame format, 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 adds an additional text stream. The text stream is mainly added at the request of the customer. Server time and some human-entered text information, there are generally two recording methods when recording two media streams. The method used here is to record the video stream and the text stream into a file, which is beneficial to the future of the file Save and review. In the aspect of acquisition software implementation, the corresponding SDK (Softwaredevelopmentkit) and API (application programming interface) are mainly applied, and VFW (VideoforWindows) is also available. However, the latter method can implement a simple single-channel video capture card. The first method is more flexible for multi-channel video collection, but the implementation is more complicated than the second.
Coordination in all aspects of the server is the key. The program starts by defaulting the video capture card channel set last time. If there is video data, it is 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 to The VGA matrix switcher sends corresponding commands to allow the VGA matrix switcher to switch the corresponding input and output channels. The corresponding input and output channels of the VGA matrix switcher can also be switched via the client via the network to the server serial port to the VGA matrix switcher (to be introduced later when the client is introduced). 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 using local area networks has been widely used in some fields. Local area networks are mostly wired local area networks, because wired local area network technology is mature and fast, but long-term transmission of large amounts of video data can also cause unstable transmission rates and data jams. The quality of the video transmission will be greatly reduced, and it will easily cause ghosting, jitter, flower screen, delay and other phenomena. The picture displayed on the server desktop is not encoded, but the video data transmitted and saved on the network is Divx encoded, which effectively reduces the burden on the network transmission and server.
In order to effectively and high-quality real-time transmission of media streams on the local area network, the support of multiple technologies is needed, including the selection of network transmission layer protocols, coding (decoding) technology, network transmission layer quality control technology, and so on.
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