You can see from Figure 8-1 how a bin has no pads of its own. This is where "ghost pads" come into play.
A ghost pad is a pad from some element in the bin that can be accessed directly from the bin as well. Compare it to a symbolic link in UNIX filesystems. Using ghost pads on bins, the bin also has a pad and can transparently be used as an element in other parts of your code.
Figure 8-2 is a representation of a
ghost pad. The sink pad of element one is now also a pad of the bin.
Because ghost pads look and work like any other pads, they can be added
to any type of elements, not just to a GstBin
,
just like ordinary pads.
A ghostpad is created using the function
gst_ghost_pad_new ()
:
#include <gst/gst.h> int main (int argc, char *argv[]) { GstElement *bin, *sink; GstPad *pad; /* init */ gst_init (&argc, &argv); /* create element, add to bin */ sink = gst_element_factory_make ("fakesink", "sink"); bin = gst_bin_new ("mybin"); gst_bin_add (GST_BIN (bin), sink); /* add ghostpad */ pad = gst_element_get_pad (sink, "sink"); gst_element_add_pad (bin, gst_ghost_pad_new ("sink", pad)); gst_object_unref (GST_OBJECT (pad)); [..] }
In the above example, the bin now also has a pad: the pad called "sink" of the given element. The bin can, from here on, be used as a substitute for the sink element. You could, for example, link another element to the bin.