What is a Real Time Video Capture Card?

Legion asks, “What makes a capture card considered “Real Time”?”
The basic definition of a real time video capture card is one that’s capable of capturing data accurately at the same rate of speed it’s receiving information. When capturing data from a tape in a VCR or video camera, this means capturing every second of audio and video information on the tape as it plays without losing any of the information in the process. In a live video scenario, real time video capture means the card is capturing and processing video received from a live camera feed as it’s happening with no additional buffering required to process the information after the fact.
Contrast this with video compression software, which often compresses video at several times less than real time in order to get a smaller file size that still looks good. The amount of processing less than real time is often a trade off between how small you need your video file to be, how quickly you need your video file, and whether the playback mechanism for the video file has any major limitations that make compressing the video file in a particular way important.