Video capture cards are responsible for converting video signals from different sources into digital signals that can be manipulated by the computer. As in the audio conversion process, the video card samples the incoming video signal by feeding it through an A-to-D (analog-to-digital) converter.

One of the jobs of the video capture card is to convert the YUV format into an RGB VGA-compatible signal. The YUV color model is used for encoding video. Y is the luminosity of the black and white signal. U and V are color difference signals. U is red minus Y (R-Y), and V is blue minus Y (B-Y).  YUV is a video encoding format that is different than RGB. An encoding circuit samples the incoming analog signal, and then performs an operation on it that is known as Color Space Conversion. Color space conversion is the process of converting the YUV signal into the RGB format acceptable to the VGA card screen memory. The resolution of a studio-quality TV signal is delivered in two interlaced screens at a rate of 60 fields per second. The encoder converts this signal scheme into a 640-by-480 (in VGA mode) image delivered to a single, non-interlaced screen at a rate of 30 or more frames per second.

In addition to changing the format, the capture card also scales the image to fit in the defined video window on the monitor screen. The capture card video signal processor adjusts the image to the correct size, by interpolating (adding or removing) adjacent pixels as necessary. The encoder samples the analog signal at a rate of 27 MB per second. This value becomes very important when considering that, at this rate, a 500 MB hard drive would be full in 18.5 seconds. To make the digitized video manageable and useful to the digital computer system, the signal must be compressed into smaller files.