What is a Video Capture Card?
A video capture card is a device that normally connects to a computer through the PCI, PCIe, or AGP ports and provides for the digitization or “capturing” of analog video signals and audio signals so that they may be processed further in some way by the computer. Newer video capture “cards” or devices that “stand alone” outside the computer may also connect by way of a USB port.
In order for a computer to display a video, the video itself must be in some sort of digital format. Most of today’s camcorders do this already, they save their movies in the form of a digital video or DV file. This file is transferred to the computer’s hard drive by connecting a USB or IEE1394 Firewire cable to the camera and computer and downloading the file contents.
However, analog video, which is basically any video that is stored in a form other than a digital file, must be converted to a digital form that the computer can understand. This is done by the use of a video capture card.
In essence, a video capture card transfers the analog video to digital video by taking several pictures of the movie each second. For standard U.S. movie capture rates the capture card takes approximately 29.9 digital pictures per second. When the movie is played back on a computer or DVD, these pictures are displayed at the same rate having the effect of moving pictures or motion video.
Types of Video Capture Cards
There are several different types of video cards based on how they connect to the computer and what functions they perform. Some computer graphics cards, that is the cards that are responsible for the display on your monitor, actually have video capture hardware built into them so they can perform both functions. Other popular types of video capture cards capture the file in various compressed formats.
The MPEG format for example, provides high quality video at a much smaller file size, but it requires a “Compression-Decompression” or CODEC process. For many computers, performing this task in addition to taking 29.9 high quality pictures per second is too much of a workload for the processor resulting in a variety of performance problems. Capture cards with the CODEC “built in” perform this process before the file is loaded into the computer, alleviating the performance load on the CPU and providing for a high quality digital video.
