Video Devices

Video devices are peripherals added to a computer to allow it to work with video. A video capture card provides a way to input video to the computer from conventional sources such as a camera, a VCR, or a TV cable or antenna. A video output card allows video to be output from the computer to a monitor. It is also possible to get video output cards that output video via a cable that can be connected directly to a television, allowing video to be played from a computer and watched on a television.

All information stored on a computer is stored in digital form as a sequence of numbers. When video is received from a source outside the computer, such as a VCR, it is usually in analog format and must be converted into digital form that can be stored in the computer. This is one of the key functions of a video capture card. To record a video sequence in digital form with the quality of a standard TV program would require approximately ninety gigabytes for one hour, equivalent to the capacity of approximately 140 CDs. A significant reduction in the required disc space, without a noticeable loss of quality, can be achieved by compressing the video. Instead of ninety gigabytes to store one hour of TV-quality video, the same information can be compressed to approximately two gigabytes. Because video is almost always stored on a computer in compressed form, most video capture cards also include hardware to perform video compression.

In the same way that the video capture card converts the incoming video to digital form, the video output card must do the opposite conversion, taking the digital video from the computer and outputting analog video for display on a monitor or television. Often the video output card will include hardware for decompression of the video as well as the conversion from digital to analog. Software running on the computer can also perform the decompression, but if the computer is not fast enough, the video will not play back smoothly.

It is also possible to get digital, as opposed to analog, video cameras. Many commercially available camcorders record compressed digital video onto tape. Such a camcorder can be connected directly to a computer without the need to use a video capture card because the video is already in a compressed digital video form. Digital video cameras are also available for connection directly to a computer. Again, because they output video in a digital format, a video capture card is not needed.

One reason to transfer video to a computer is to allow for editing. Once the video is stored on the computer, sophisticated editing software can be used to manipulate the video. For example, holiday camcorder recordings typically contain much unwanted material. After transferring the video from the camcorder to a computer, the video can be edited to remove the unwanted parts. When the editing is finished, the holiday video can be transferred back to the camcorder tapes or to a standard VCR. Or, the edited video can be kept on the computer and played from the computer to a monitor or television.

If a computer is equipped with both a camera and a video output card, it can be used for video conferencing. In video conferencing, two or more people in different locations communicate with each other using both sound and video through their computers. The camera captures a digital video signal of the person, and the computer transmits it through a network to the other participants. Similarly, the other participants have cameras so that video is transmitted to them also. Each person also needs a video output card to display the video received from the other video conference participants. Video conferencing allows people to both see and hear each other while in remote locations.

When a computer is equipped to handle video, it can be used to perform functions normally done by consumer electronics devices. If a computer includes a digital versatile disc read-only memory (DVD-ROM) drive and a suitable video output card, it is possible to play DVD videos on the computer. Or, the output from the video card can be connected to a television and the DVDs can be watched on the television instead of the computer monitor.