X Video Extension

The X video extension, often abbreviated as XVideo or Xv, is a video output mechanism for the X Window System. The protocol was designed by David Carver; the specification for version 2 of the protocol was written in July 1991. Its main use today is to rescale video playback in the video controller hardware, in order to enlarge a given video or to watch it in full screen mode. Without XVideo, X would have to do this scaling on the main CPU. That requires a considerable amount of processing power, sometimes to the point of slowing down/degrading the video stream; the video controller is specifically designed for this kind of computation, so can do it much more cheaply. Similarly, the X video extension has the video controller perform color space conversions. It can also have the controller change contrast, brightness and hue of a displayed video stream.

In order for this to work, three things have to come together:

• The video controller has to provide the required functions.
• The device driver software for the video controller and the X server program have to implement the XVideo interface.
• The video playback software has to make use of this interface.

Most modern video controllers provide the functions required for XVideo; the feature is known as hardware scaling and YUV acceleration or sometimes as 2D hardware acceleration. The XFree86 X server has implemented XVideo since version 4.0.2. To check whether a given X server supports XVideo, one can use the utility xdpyinfo. To check whether the video controller provides the required functions and whether the X device driver implements XVideo for any of them, one can use the xvinfo program.