XvQueryExtension man page
XvQueryExtension — return version and release of extension
int XvQueryExtension(Display *dpy, unsigned int *p_version, unsigned int *p_revision, unsigned int *p_request_base, unsigned int *p_event_base, unsigned int *p_error_base);
Specifies the connection to the X server.
Pointer to where the current version number of the Xv video extension is written.
Pointer to where the revision number of the Xv video extension is written.
Pointer to where the extension major request number is returned
Pointer to where the extension event base is returned
Pointer to where the extension error base is returned
XvQueryExtension(3) returns the version and release numbers for the Xv video extension currently loaded on the system. The extension major request number, event base, and error base are also returned.
Returned if XvQueryExtension(3) completed successfully.
Returned if the Xv video extension is not available for the named display.