Just as the ALSA system provides kernel drivers and a programming framework for your audio gadgets, there are two important components involved in getting your cameras to work under Linux:
The Linux USB Video Class (UVC) drivers provide the low-level functions for your USB webcam, which are in accordance with a specification followed by most webcams produced today.
Video4Linux (V4L) is a video capture framework used by applications that record video from cameras, TV tuners, and other video producing devices. There's an updated version of V4L called V4L2, which we'll want to use whenever possible.
