The X Video Extension (Xv) extension provides support for video adaptors attached to an X display. It takes the approach that a display may have one or more video adaptors, each of which has one or more ports through which independent video streams pass.
An adaptor may be able to display video in a drawable, capture video from a drawable, or both. It translates between video encoding (NTSC, PAL, SECAM, etc...) and drawable format (depth and visual-id pair). An adaptor may support multiple video encodings and/or multiple drawable formats.
Clients use Xv(3) to gain access and manage sharing of a display's video resources. Typically, a client will use XvQueryExtension(3) to determine the status of the extension, XvQueryAdaptors(3) to get a description of what video adaptors exist, and XvQueryEncodings(3) to get a description of what video encodings an adaptor supports.
Once a client has determined what video resources are available, it is free to put video into a drawable or get video from a drawable, according the capabilities supported. Clients can select to receive events when video activity changes in a drawable and when port attributes have changed.
The Xv protocol version 2.2 and later is extended to support client images in alternate colorspaces (XvImages). Xv adaptors which are capable of displaying XvImages will have the XvImageMask field set in the type field of the XvAdaptorInfo. XvImage formats supported by the port may be queried with XvListImageFormats(3). XvImages may be created with the help of XvCreateImage(3) or XvShmCreateImage(3); XvImages may be displayed with XvPutImage(3) or XvShmPutImage(3). The Port attributes of the port specified in the Xv(Shm)PutImage command will be valid for the image operation when applicable. There will be a port encoding with the name "XV_IMAGE". The width and height of that encoding will indicate the maximum source image size.
Summary of Library Functions
The following is a summary of Xv library functions and events:
XvCreateImage(3) - create an XvImage
XvGetPortAttribute(3) - return current port attribute value
XvGetStill(3) - capture a single frame of video from a drawable
XvGetVideo(3) - capture video from a drawable
XvGrabPort(3) - lock port for exclusive use by client
XvListImageFormats(3) - return list of image formats for a port
XvPortNotify(3) - event generated when port attributes change
XvPutImage(3) - write a XvImage to a drawable
XvPutStill(3) - write a single frame of video to a drawable
XvPutVideo(3) - write video into a drawable
XvQueryAdaptors(3) - return adaptor information for a screen
XvQueryBestSize(3) - determine the optimum drawable region size
XvQueryEncodings(3) - return list of encodings for an adaptor
XvQueryExtension(3) - return version and revision of extension
XvQueryPortAttributes(3) - return list of attributes of a port
XvSelectPortNotify(3) - enable or disable XvPortNotify events
XvSelectVideoNotify(3) - enable or disable XvVideoNotify events
XvSetPortAttribute(3) - set an attribute for a port
XvShmCreateImage(3) - create an XvImage in shared memory
XvShmPutImage(3) - write a XvImage in shared memory to a drawable
XvStopVideo(3) - stop active video
XvUngrabPort(3) - release a grabbed port
XvVideoNotify(3) - event generated for video processing
Each of these functions and events is described in its own Xv man page.