Chapter 19. Components

GStreamer includes several higher-level components to simplify your applications life. All of the components discussed here (for now) are targetted at media playback. The idea of each of these components is to integrate as closely as possible with a GStreamer pipeline, but to hide the complexity of media type detection and several other rather complex topics that have been discussed in Part III in GStreamer Application Development Manual (0.10.14).

We currently recommend people to use either playbin (see Section 19.1) or decodebin (see Section 19.2), depending on their needs. Playbin is the recommended solution for everything related to simple playback of media that should just work. Decodebin is a more flexible autoplugger that could be used to add more advanced featuers, such as playlist support, crossfading of audio tracks and so on. Its programming interface is more low-level than that of playbin, though.

19.1. Playbin

Playbin is an element that can be created using the standard GStreamer API (e.g. gst_element_factory_make ()). The factory is conveniently called "playbin". By being a GstPipeline (and thus a GstElement), playbin automatically supports all of the features of this class, including error handling, tag support, state handling, getting stream positions, seeking, and so on.

Setting up a playbin pipeline is as simple as creating an instance of the playbin element, setting a file location (this has to be a valid URI, so "<protocol>://<location>", e.g. file:///tmp/my.ogg or http://www.example.org/stream.ogg) using the "uri" property on playbin, and then setting the element to the GST_STATE_PLAYING state. Internally, playbin will set up a pipeline to playback the media location.


#include <gst/gst.h>

[.. my_bus_callback goes here ..]

gint
main (gint   argc,
      gchar *argv[])
{
  GMainLoop *loop;
  GstElement *play;
  GstBus *bus;

  /* init GStreamer */
  gst_init (&argc, &argv);
  loop = g_main_loop_new (NULL, FALSE);

  /* make sure we have a URI */
  if (argc != 2) {
    g_print ("Usage: %s <URI>\n", argv[0]);
    return -1;
  }

  /* set up */
  play = gst_element_factory_make ("playbin", "play");
  g_object_set (G_OBJECT (play), "uri", argv[1], NULL);

  bus = gst_pipeline_get_bus (GST_PIPELINE (play));
  gst_bus_add_watch (bus, my_bus_callback, loop);
  gst_object_unref (bus);

  gst_element_set_state (play, GST_STATE_PLAYING);

  /* now run */
  g_main_loop_run (loop);

  /* also clean up */
  gst_element_set_state (play, GST_STATE_NULL);
  gst_object_unref (GST_OBJECT (play));

  return 0;
}
    

Playbin has several features that have been discussed previously:

For convenience, it is possible to test "playbin" on the commandline, using the command "gst-launch-0.10 playbin uri=file:///path/to/file".