Linking elements

By linking a source element with zero or more filter-like elements and finally a sink element, you set up a media pipeline. Data will flow through the elements. This is the basic concept of media handling in GStreamer.

By linking these three elements, we have created a very simple chain of elements. The effect of this will be that the output of the source element ("element1") will be used as input for the filter-like element ("element2"). The filter-like element will do something with the data and send the result to the final sink element ("element3").

Imagine the above graph as a simple Ogg/Vorbis audio decoder. The source is a disk source which reads the file from disc. The second element is a Ogg/Vorbis audio decoder. The sink element is your soundcard, playing back the decoded audio data. We will use this simple graph to construct an Ogg/Vorbis player later in this manual.

In code, the above graph is written like this:

#include <gst/gst.h>

int
main (int   argc,
      char *argv[])
{
  GstElement *pipeline;
  GstElement *source, *filter, *sink;

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

  /* create pipeline */
  pipeline = gst_pipeline_new ("my-pipeline");

  /* create elements */
  source = gst_element_factory_make ("fakesrc", "source");
  filter = gst_element_factory_make ("identity", "filter");
  sink = gst_element_factory_make ("fakesink", "sink");

  /* must add elements to pipeline before linking them */
  gst_bin_add_many (GST_BIN (pipeline), source, filter, sink, NULL);

  /* link */
  if (!gst_element_link_many (source, filter, sink, NULL)) {
    g_warning ("Failed to link elements!");
  }

[..]

}
    

For more specific behaviour, there are also the functions gst_element_link () and gst_element_link_pads (). You can also obtain references to individual pads and link those using various gst_pad_link_* () functions. See the API references for more details.

Important: you must add elements to a bin or pipeline before linking them, since adding an element to a bin will disconnect any already existing links. Also, you cannot directly link elements that are not in the same bin or pipeline; if you want to link elements or pads at different hierarchy levels, you will need to use ghost pads (more about ghost pads later).