The video capture card is widely used in the current monitoring field, so what function does the capture card have in the end? This article is for you to answer from the technical point of view!
Two types of video capture card
Now as long as you buy a DVR card, the shop owner generally asks you what kind of card you want - a soft card or a hard card. Here we will first introduce the difference between a soft card and a hard card.
First, soft compression DVR
With soft card DVR we are generally called soft compression DVR, in fact, is a video capture card, with the card is equipped with monitoring software to achieve video surveillance, video, playback history video and remote monitoring functions, the hardware is one or more video capture chip (such as: fusion878a, saa7130/7134, tw6802B/6805, etc.) Receive signals from analog cameras, convert them to digital signals, and then directly or through the PCI bridge chip from the PCI gold finger into the motherboard, the original digital video signal, executed in memory The CPU instruction computes, compresses and processes the video, and stores it on the hard disk. In addition raw video data is sent directly to the video card and previewed by the monitor.
The circuit board of the soft card is very simple, there is no compressed chip and temporary storage chip on the board, the cost is low, generally about 1/3 of the hard compression, so the price is its greatest advantage, and in addition, we can see from the principle that the soft compression DVR There is a CPU for compression, so its compression quality is good, and its video resolution is high. With ample CPU resources, soft-compressed DVRs are no less than hard-compressed DVRs in terms of video, network, and other functions.
Second, hard compression DVR
Hard-compressed DVR, also known as video capture compression card, is basically the same as the soft-compression principle. The difference is that after the analog video is converted to a digital signal, it is not directly sent to the motherboard, graphics card, and memory through PCI, but is first compressed by hardware. The DVR card's own DSP replaces the computer's CPU to execute compression algorithm instructions, compress the memory chip on the DVR card, and then enter the motherboard through the PCI gold finger. Therefore, the hard-compressed DVR circuit board has more DSP or other compression chips and memory chips. Therefore, the main advantages of hard-compressed DVRs are mainly in the monitoring of large numbers. For example, 32-channel full-real-time surveillance video is difficult to achieve. This market gap can be occupied by hard compression.
Video capture card function technology
Interfaces: Currently, the interfaces of video capture cards on the market can be divided into several types. The interfaces of video capture cards include interfaces between video and PCs and interfaces with analog video equipment. At present, the PC video capture card usually uses a 32-bit PCI bus interface. It is inserted into the expansion slot of the PC motherboard to achieve the communication and data transmission between the capture card and the PC. The capture card must have at least one composite video interface (VideoIn) for connection to analog video equipment. High-performance capture cards typically 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 the video capture card generally does not have a TV antenna interface and an audio input interface. It cannot use a video capture card to directly collect TV RF signals. At the same time, it cannot directly capture the audio signals in analog video. To acquire sound, a sound card must be installed on the PC. The video capture card uses the sound card on the PC to obtain the digitized sound 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. The signal is collected, quantized into a digital signal, and then compressed into a digital video sequence. Most video capture cards have the function of hardware compression. When the video signal is collected, 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.
Since the analog video input can provide an uninterrupted source of information, the video capture card captures each frame of the video in the analog video sequence and passes the data to the PC system before acquiring the next frame of the image. Therefore, the key to achieving 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 occurs, ie, a frame dropping phenomenon. The acquisition card first compresses the acquired video sequence and then stores it in the hard disk, which means that the acquisition and compression of the video sequence are completed together, eliminating the inconvenience of performing compression processing again. Different grades of acquisition cards have different quality acquisition and compression performance.
Drivers and Applications: Some video capture cards need to be driven before they can be used normally. Video capture cards are generally equipped with hardware drivers to implement PC control and data communication on the capture card. According to the operating system environment required by different capture cards, there are different drivers. Only after you insert the capture card into the motherboard's expansion slot of the PC and properly install the driver, can it work properly. Capture cards are generally equipped with acquisition applications to control and operate the acquisition process. There are also some common acquisition programs. Digital video editing software such as Adobe Premiere also has acquisition functions, but these application software must be used with the acquisition card hardware. That is, only the acquisition card hardware can be used after it is properly installed and driven.
Application of video capture card
Electronic devices have gone from being obscure to people’s daily lives. People are always confused when faced with ever-changing monitoring products on the market and constantly updated monitoring card prices, so we only have to constantly understand the monitoring market and monitoring. Technology is invincible.
With the continuous development of information technology, computer technology has introduced video capture, video processing, computer video processing and digital transmission of video data has been widely used in many areas, and has also been widely used in our aircraft flight test. There are many methods for capturing video images, which can be basically divided into two categories: digital signal acquisition and analog signal acquisition.
The use of image acquisition chipset to complete the image acquisition, frame memory address generation and image data refresh; in addition to the acquisition mode to be set, the main processor does not participate in the acquisition process, we just take out the collected in the corresponding frame memory address The video data can get the corresponding video data. This method has been significantly improved in terms of functions, performance, reliability, speed and other aspects, but the cost is high. The latter adopts a general-purpose video A/D converter to achieve image acquisition. Its characteristic is that the data acquisition takes up CPU time, has high requirements on the speed of the processor, is low in cost and easy to implement, and can meet the needs of certain image acquisition systems.
This system requires a maximum of 25 frames per second (set as adjustable), the client real-time display maximum 25 frames (set to adjustable), save as MPEG4 format, the screen requires a maximum resolution of 1024X768. Multi-channel video real-time acquisition uses the VisionRGB-PRO card (Datapath, UK). This card can capture two video data in real time at the same time, basically meeting the requirements of the system, and then using a VGA matrix switcher to the front-end data source. Four-channel video data is manually switched.
Hardware environment construction
This acquisition system mainly realizes artificial switching real-time acquisition of front-end four-channel video data. At the server side, two video data can be collected and stored at the same time (only one video capture card is used here), and only one video data can be collected at one time. It is transmitted to the client through the network in real time, and the server also displays the collected video in real time. In the video switching, it can be switched between the server and the client. In the server, the VGA matrix switch can be used to switch the corresponding video input and output ports. 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.
Large amount of video data, which requires video data processing system with real-time acquisition, large-capacity storage and real-time processing features. The software must realize the real-time acquisition of video data (up to two channels), control the video interface, encode 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 it also undertakes a lot of work. Therefore, the requirements on software and hardware are also very high. The above is the main function to be implemented on the server.
The most important aspect of the acquisition is real-time. In this case, the data is acquired from the port in an event-driven manner. The video data stream is collected and stored on the desktop while it is being encoded. The data collected by the video must be passed to the corresponding module of the software. Bitmap-type video frames are set to facilitate display and encoding preservation on the server side. Divx encoding is used here. Divx encoding forms an MPEG4 stream in frame format.
Server-side implementation
Divx decoding is also decompressed in the format of a frame, so it is advantageous to send video data streams in units of 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 two video streams are collected by the video card. When the video stream is saved, a text stream is added. The text stream is mainly added to the customer's request. The server time and some human-entered textual information generally have two recording methods when recording two media streams. In this case, the video stream and the text stream are recorded in a file, which is advantageous for the file. Save and review. 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 collecting multiple video signals is more flexible, but the implementation is more complicated than the second one.
Coordinating work in all aspects of the server is the key, the program starts first by default the last set of video capture card channel, if there is video data to display, save, if there is no video data to wait, if you want to adjust the video capture card channel available serial port to The VGA matrix switcher sends the corresponding command for the VGA matrix switcher to switch the corresponding input and output channels. You can also switch the corresponding input and output channels of the VGA matrix switcher via the client to the VGA matrix switcher via the network to the server (described later in the introduction of the client). 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 real-time transmission of video data over local area networks has been applied in a large number of applications. LANs are mostly wired LANs because wired LAN technology is mature and transmission speeds are high. However, when a large amount of video data is transmitted for a long period of time, the transmission rate is unstable, causing data congestion. The quality of video transmission will be greatly reduced, and it will easily cause ghosting, jitter, framing, and delay. The screen displayed on the server desktop is not encoded, but the video data transmitted and saved on the network is Divx-encoded, which effectively relieves the burden of network transmission and server.
In order to effectively transmit high-quality real-time media streams on the LAN, multiple technologies are required, including the selection of network transport layer protocols, coding (de-)coding techniques, and network transport layer quality control technologies.
Two types of video capture card
Now as long as you buy a DVR card, the shop owner generally asks you what kind of card you want - a soft card or a hard card. Here we will first introduce the difference between a soft card and a hard card.
First, soft compression DVR
With soft card DVR we are generally called soft compression DVR, in fact, is a video capture card, with the card is equipped with monitoring software to achieve video surveillance, video, playback history video and remote monitoring functions, the hardware is one or more video capture chip (such as: fusion878a, saa7130/7134, tw6802B/6805, etc.) Receive signals from analog cameras, convert them to digital signals, and then directly or through the PCI bridge chip from the PCI gold finger into the motherboard, the original digital video signal, executed in memory The CPU instruction computes, compresses and processes the video, and stores it on the hard disk. In addition raw video data is sent directly to the video card and previewed by the monitor.
The circuit board of the soft card is very simple, there is no compressed chip and temporary storage chip on the board, the cost is low, generally about 1/3 of the hard compression, so the price is its greatest advantage, and in addition, we can see from the principle that the soft compression DVR There is a CPU for compression, so its compression quality is good, and its video resolution is high. With ample CPU resources, soft-compressed DVRs are no less than hard-compressed DVRs in terms of video, network, and other functions.
Second, hard compression DVR
Hard-compressed DVR, also known as video capture compression card, is basically the same as the soft-compression principle. The difference is that after the analog video is converted to a digital signal, it is not directly sent to the motherboard, graphics card, and memory through PCI, but is first compressed by hardware. The DVR card's own DSP replaces the computer's CPU to execute compression algorithm instructions, compress the memory chip on the DVR card, and then enter the motherboard through the PCI gold finger. Therefore, the hard-compressed DVR circuit board has more DSP or other compression chips and memory chips. Therefore, the main advantages of hard-compressed DVRs are mainly in the monitoring of large numbers. For example, 32-channel full-real-time surveillance video is difficult to achieve. This market gap can be occupied by hard compression.
Video capture card function technology
Interfaces: Currently, the interfaces of video capture cards on the market can be divided into several types. The interfaces of video capture cards include interfaces between video and PCs and interfaces with analog video equipment. At present, the PC video capture card usually uses a 32-bit PCI bus interface. It is inserted into the expansion slot of the PC motherboard to achieve the communication and data transmission between the capture card and the PC. The capture card must have at least one composite video interface (VideoIn) for connection to analog video equipment. High-performance capture cards typically 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 the video capture card generally does not have a TV antenna interface and an audio input interface. It cannot use a video capture card to directly collect TV RF signals. At the same time, it cannot directly capture the audio signals in analog video. To acquire sound, a sound card must be installed on the PC. The video capture card uses the sound card on the PC to obtain the digitized sound 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. The signal is collected, quantized into a digital signal, and then compressed into a digital video sequence. Most video capture cards have the function of hardware compression. When the video signal is collected, 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.
Since the analog video input can provide an uninterrupted source of information, the video capture card captures each frame of the video in the analog video sequence and passes the data to the PC system before acquiring the next frame of the image. Therefore, the key to achieving 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 occurs, ie, a frame dropping phenomenon. The acquisition card first compresses the acquired video sequence and then stores it in the hard disk, which means that the acquisition and compression of the video sequence are completed together, eliminating the inconvenience of performing compression processing again. Different grades of acquisition cards have different quality acquisition and compression performance.
Drivers and Applications: Some video capture cards need to be driven before they can be used normally. Video capture cards are generally equipped with hardware drivers to implement PC control and data communication on the capture card. According to the operating system environment required by different capture cards, there are different drivers. Only after you insert the capture card into the motherboard's expansion slot of the PC and properly install the driver, can it work properly. Capture cards are generally equipped with acquisition applications to control and operate the acquisition process. There are also some common acquisition programs. Digital video editing software such as Adobe Premiere also has acquisition functions, but these application software must be used with the acquisition card hardware. That is, only the acquisition card hardware can be used after it is properly installed and driven.
Application of video capture card
Electronic devices have gone from being obscure to people’s daily lives. People are always confused when faced with ever-changing monitoring products on the market and constantly updated monitoring card prices, so we only have to constantly understand the monitoring market and monitoring. Technology is invincible.
With the continuous development of information technology, computer technology has introduced video capture, video processing, computer video processing and digital transmission of video data has been widely used in many areas, and has also been widely used in our aircraft flight test. There are many methods for capturing video images, which can be basically divided into two categories: digital signal acquisition and analog signal acquisition.
The use of image acquisition chipset to complete the image acquisition, frame memory address generation and image data refresh; in addition to the acquisition mode to be set, the main processor does not participate in the acquisition process, we just take out the collected in the corresponding frame memory address The video data can get the corresponding video data. This method has been significantly improved in terms of functions, performance, reliability, speed and other aspects, but the cost is high. The latter adopts a general-purpose video A/D converter to achieve image acquisition. Its characteristic is that the data acquisition takes up CPU time, has high requirements on the speed of the processor, is low in cost and easy to implement, and can meet the needs of certain image acquisition systems.
This system requires a maximum of 25 frames per second (set as adjustable), the client real-time display maximum 25 frames (set to adjustable), save as MPEG4 format, the screen requires a maximum resolution of 1024X768. Multi-channel video real-time acquisition uses the VisionRGB-PRO card (Datapath, UK). This card can capture two video data in real time at the same time, basically meeting the requirements of the system, and then using a VGA matrix switcher to the front-end data source. Four-channel video data is manually switched.
Hardware environment construction
This acquisition system mainly realizes artificial switching real-time acquisition of front-end four-channel video data. At the server side, two video data can be collected and stored at the same time (only one video capture card is used here), and only one video data can be collected at one time. It is transmitted to the client through the network in real time, and the server also displays the collected video in real time. In the video switching, it can be switched between the server and the client. In the server, the VGA matrix switch can be used to switch the corresponding video input and output ports. 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.
Large amount of video data, which requires video data processing system with real-time acquisition, large-capacity storage and real-time processing features. The software must realize the real-time acquisition of video data (up to two channels), control the video interface, encode 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 it also undertakes a lot of work. Therefore, the requirements on software and hardware are also very high. The above is the main function to be implemented on the server.
The most important aspect of the acquisition is real-time. In this case, the data is acquired from the port in an event-driven manner. The video data stream is collected and stored on the desktop while it is being encoded. The data collected by the video must be passed to the corresponding module of the software. Bitmap-type video frames are set to facilitate display and encoding preservation on the server side. Divx encoding is used here. Divx encoding forms an MPEG4 stream in frame format.
Server-side implementation
Divx decoding is also decompressed in the format of a frame, so it is advantageous to send video data streams in units of 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 two video streams are collected by the video card. When the video stream is saved, a text stream is added. The text stream is mainly added to the customer's request. The server time and some human-entered textual information generally have two recording methods when recording two media streams. In this case, the video stream and the text stream are recorded in a file, which is advantageous for the file. Save and review. 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 collecting multiple video signals is more flexible, but the implementation is more complicated than the second one.
Coordinating work in all aspects of the server is the key, the program starts first by default the last set of video capture card channel, if there is video data to display, save, if there is no video data to wait, if you want to adjust the video capture card channel available serial port to The VGA matrix switcher sends the corresponding command for the VGA matrix switcher to switch the corresponding input and output channels. You can also switch the corresponding input and output channels of the VGA matrix switcher via the client to the VGA matrix switcher via the network to the server (described later in the introduction of the client). 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 real-time transmission of video data over local area networks has been applied in a large number of applications. LANs are mostly wired LANs because wired LAN technology is mature and transmission speeds are high. However, when a large amount of video data is transmitted for a long period of time, the transmission rate is unstable, causing data congestion. The quality of video transmission will be greatly reduced, and it will easily cause ghosting, jitter, framing, and delay. The screen displayed on the server desktop is not encoded, but the video data transmitted and saved on the network is Divx-encoded, which effectively relieves the burden of network transmission and server.
In order to effectively transmit high-quality real-time media streams on the LAN, multiple technologies are required, including the selection of network transport layer protocols, coding (de-)coding techniques, and network transport layer quality control technologies.
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