Can be used to pass custom connector properties to DRM. Properties can
be enumerated using modetest tool. These properties can then be applied
with the following gst-launch-1.0 syntax. Note that the name of the
structure is ignored.
... ! kmssink connector-properties="s,props1=value,props2=value"
https://bugzilla.gnome.org/show_bug.cgi?id=797027