The following is a summary of Xv library functions:
XvGetPortAttribute(3X) - return current port attribute value
XvGetStill(3X) - capture a single frame of video from a drawable
XvGetVideo(3X) - capture video from a drawable
XvGrabPort(3X) - lock port for exclusive use by client
XvPortNotify(3X) - event generated when port attributes change
XvPutStill(3X) - write a single frame of video to a drawable
XvPutVideo(3X) - write video into a drawable
XvQueryAdaptors(3X) - return adaptor information for a screen
XvQueryBestSize(3X) - determine the optimum drawable region size
XvQueryEncodings(3X) - return list of encodings for an adaptor
XvQueryExtension(3X) - return version and revision of extension
XvSelectPortNotify(3X) - enable or disable XvPortNotify events
XvSelectVideoNotify(3X) - enable or disable XvVideoNotify events
XvSetPortAttribute(3X) - set an attribute for a port
XvStopVideo(3X) - stop active video
XvUngrabPort(3X) - release a grabbed port
XvVideoNotify(3X) - event generated for video processing
Each of these functions is described in its own Xv man page.