&GStreamer; includes several higher-level components to simplify an application developer's 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 . We currently recommend people to use either playbin (see ) or decodebin (see ), 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 features, such as playlist support, crossfading of audio tracks and so on. Its programming interface is more low-level than that of playbin, though. 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 using the uri property on playbin, and then setting the element to the GST_STATE_PLAYING state (the location has to be a valid URI, so <protocol>://<location>, e.g. file:///tmp/my.ogg or http://www.example.org/stream.ogg). 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: Settable video and audio output (using the video-sink and audio-sink properties). Mostly controllable and trackable as a GstElement, including error handling, eos handling, tag handling, state handling (through the GstBus), media position handling and seeking. Buffers network-sources, with buffer fullness notifications being passed through the GstBus. Supports visualizations for audio-only media. Supports subtitles, both in the media as well as from separate files. For separate subtitle files, use the suburi property. Supports stream selection and disabling. If your media has multiple audio or subtitle tracks, you can dynamically choose which one to play back, or decide to turn it off alltogther (which is especially useful to turn off subtitles). For each of those, use the current-text and other related properties. For convenience, it is possible to test playbin on the commandline, using the command gst-launch-0.10 playbin uri=file:///path/to/file. Decodebin is the actual autoplugger backend of playbin, which was discussed in the previous section. Decodebin will, in short, accept input from a source that is linked to its sinkpad and will try to detect the media type contained in the stream, and set up decoder routines for each of those. It will automatically select decoders. For each decoded stream, it will emit the new-decoded-pad signal, to let the client know about the newly found decoded stream. For unknown streams (which might be the whole stream), it will emit the unknown-type signal. The application is then responsible for reporting the error to the user. #include <gst/gst.h> [.. my_bus_callback goes here ..] GstElement *pipeline, *audio; static void cb_newpad (GstElement *decodebin, GstPad *pad, gboolean last, gpointer data) { GstCaps *caps; GstStructure *str; GstPad *audiopad; /* only link once */ audiopad = gst_element_get_static_pad (audio, "sink"); if (GST_PAD_IS_LINKED (audiopad)) { g_object_unref (audiopad); return; } /* check media type */ caps = gst_pad_get_caps (pad); str = gst_caps_get_structure (caps, 0); if (!g_strrstr (gst_structure_get_name (str), "audio")) { gst_caps_unref (caps); gst_object_unref (audiopad); return; } gst_caps_unref (caps); /* link'n'play */ gst_pad_link (pad, audiopad); } gint main (gint argc, gchar *argv[]) { GMainLoop *loop; GstElement *src, *dec, *conv, *sink; GstPad *audiopad; GstBus *bus; /* init GStreamer */ gst_init (&argc, &argv); loop = g_main_loop_new (NULL, FALSE); /* make sure we have input */ if (argc != 2) { g_print ("Usage: %s <filename>\n", argv[0]); return -1; } /* setup */ pipeline = gst_pipeline_new ("pipeline"); bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline)); gst_bus_add_watch (bus, my_bus_callback, loop); gst_object_unref (bus); src = gst_element_factory_make ("filesrc", "source"); g_object_set (G_OBJECT (src), "location", argv[1], NULL); dec = gst_element_factory_make ("decodebin", "decoder"); g_signal_connect (dec, "new-decoded-pad", G_CALLBACK (cb_newpad), NULL); gst_bin_add_many (GST_BIN (pipeline), src, dec, NULL); gst_element_link (src, dec); /* create audio output */ audio = gst_bin_new ("audiobin"); conv = gst_element_factory_make ("audioconvert", "aconv"); audiopad = gst_element_get_static_pad (conv, "sink"); sink = gst_element_factory_make ("alsasink", "sink"); gst_bin_add_many (GST_BIN (audio), conv, sink, NULL); gst_element_link (conv, sink); gst_element_add_pad (audio, gst_ghost_pad_new ("sink", audiopad)); gst_object_unref (audiopad); gst_bin_add (GST_BIN (pipeline), audio); /* run */ gst_element_set_state (pipeline, GST_STATE_PLAYING); g_main_loop_run (loop); /* cleanup */ gst_element_set_state (pipeline, GST_STATE_NULL); gst_object_unref (GST_OBJECT (pipeline)); return 0; } Decodebin, similar to playbin, supports the following features: Can decode an unlimited number of contained streams to decoded output pads. Is handled as a GstElement in all ways, including tag or error forwarding and state handling. Although decodebin is a good autoplugger, there's a whole lot of things that it does not do and is not intended to do: Taking care of input streams with a known media type (e.g. a DVD, an audio-CD or such). Selection of streams (e.g. which audio track to play in case of multi-language media streams). Overlaying subtitles over a decoded video stream. Decodebin can be easily tested on the commandline, e.g. by using the command gst-launch-0.8 filesrc location=file.ogg ! decodebin ! audioconvert ! alsasink.