There are three types of capture devices: digital, analog and DV/HDV cameras. All three have different hardware requirements.
DV/HDV cameras: In the case of a DV or HDV camera, the video signal is sent to the PC in digital format. All you need to transfer video to your PC is a connecting cable and a corresponding socket on your PC.
Analog Video: Video signals from an analog source need to be converted to a digital format for your PC to be able to work with them. Examples of analog capture devices include VHS video recorders, TV, VHS-C, 8 mm, and Hi-8 video cameras. Unlike DV capture devices where the device itself delivers digital video signals to your PC, you need to have a video capture card installed in the PC in the case of analog video signals. The analog signals are converted into digital signals by the video capture card.
Digital Video (ATSC, DVB-T/S/C): Video signals from digital capture devices are sent to the PC in digital format and exist in MPEG-2 format after transfer. TV cards are typical examples of digital devices. In order to transfer digital video, a corresponding device must be connected to your PC.