7.4. Ghost pads

You can see from Figure 7-1 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 7-2 is a representation of a ghost pad. The sink pad of element one is now also a pad of the bin. Obviously, ghost pads can be added to any type of elements, not just to a GstBin.

A ghostpad is created using the function gst_element_add_ghost_pad ():

#include <gst/gst.h>

int
main (int   argc,
      char *argv[])
{
  GstElement *bin, *sink;

  /* init */
  gst_init (&argc, &argv);

  /* create element, add to bin, add ghostpad */
  sink = gst_element_factory_make ("fakesink", "sink");
  bin = gst_bin_new ("mybin");
  gst_bin_add (GST_BIN (bin), sink);
  gst_element_add_ghost_pad (bin,
      gst_element_get_pad (sink, "sink"), "sink");

[..]

}
    

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.