XvQueryPortAttributes - return list of attributes of a video port
#include <X11/extensions/Xvlib.h>
XvAttribute* XvQueryPortAttributes(Display *dpy,
                 XvPortID port,  int *p_num_attributes);
  - dpy
- Specifies the connection to the X server.
- port
- Specifies the port whose adaptor is to be queried for its list of
      attributes.
- p_num_attributes
- A pointer to where the number of attributes returned in the array is
      written.
XvQueryPortAttributes(3)returnsthenumberofattributes
  and an array of XvAttributes valid for the given port. The array may be freed
  with XFree(3).
XvAttribute has the following structure:
    typedef struct {
      int flags;
      int min_value;
      int max_value;
      char *name;
    } XvAttribute;
  - flags
- May be XvGettable or XvSettable or both OR'd together indicating the
      particular attribute is readable, writeable or readable and
    writeable.
- min_value
- The minimum attribute values which are valid for the driver.
- The maximum attribute values which are valid for the driver.
- name
- A string describing the name of the attribute that may be used to retrieve
      the Atom for the particular attribute.
  - [XvBadPort]
- Generated if the requested port does not exist.
XvGetPortAttribute(3), XvSetPortAttribute(3)