Adds a filter for which gstreamer.Device will be monitored, any device that matches
all these classes and the gstreamer.Caps will be returned.
If this function is called multiple times to add more filters, each will be
matched independently. That is, adding more filters will not further restrict
what devices are matched.
The gstreamer.Caps supported by the device as returned by Device.getCaps are
not intersected with caps filters added using this function.
Filters must be added before the gstreamer.DeviceMonitor is started.
device classes to use as filter or NULL for any class
the gstreamer.Caps to filter or NULL for ANY
The id of the new filter or 0 if no provider matched the filter's