playbin

playbin — Autoplug and play media from an uri

Synopsis

struct              GstPlayBin;

Object Hierarchy

  GObject
   +----GstObject
         +----GstElement
               +----GstBin
                     +----GstPipeline
                           +----GstPlayBaseBin
                                 +----GstPlayBin

Implemented Interfaces

GstPlayBin implements GstChildProxy.

Properties

  "audio-sink"               GstElement*           : Read / Write
  "frame"                    GstBuffer*            : Read
  "subtitle-font-desc"       gchar*                : Write
  "video-sink"               GstElement*           : Read / Write
  "vis-plugin"               GstElement*           : Read / Write
  "volume"                   gdouble               : Read / Write
  "connection-speed"         guint                 : Read / Write

Description

Playbin provides a stand-alone everything-in-one abstraction for an audio and/or video player.

Note

This element is deprecated and no longer supported. You should use the playbin2 element instead.

It can handle both audio and video files and features

  • automatic file type recognition and based on that automatic selection and usage of the right audio/video/subtitle demuxers/decoders
  • visualisations for audio files
  • subtitle support for video files
  • stream selection between different audio/subtitles streams
  • meta info (tag) extraction
  • easy access to the last video frame
  • buffering when playing streams over a network
  • volume control

Usage

A playbin element can be created just like any other element using gst_element_factory_make(). The file/URI to play should be set via the "uri" property. This must be an absolute URI, relative file paths are not allowed. Example URIs are file:///home/joe/movie.avi or http://www.joedoe.com/foo.ogg

Playbin is a GstPipeline. It will notify the application of everything that's happening (errors, end of stream, tags found, state changes, etc.) by posting messages on its GstBus. The application needs to watch the bus.

Playback can be initiated by setting the element to PLAYING state using gst_element_set_state(). Note that the state change will take place in the background in a separate thread, when the function returns playback is probably not happening yet and any errors might not have occured yet. Applications using playbin should ideally be written to deal with things completely asynchroneous.

When playback has finished (an EOS message has been received on the bus) or an error has occured (an ERROR message has been received on the bus) or the user wants to play a different track, playbin should be set back to READY or NULL state, then the "uri" property should be set to the new location and then playbin be set to PLAYING state again.

Seeking can be done using gst_element_seek_simple() or gst_element_seek() on the playbin element. Again, the seek will not be executed instantaneously, but will be done in a background thread. When the seek call returns the seek will most likely still be in process. An application may wait for the seek to finish (or fail) using gst_element_get_state() with -1 as the timeout, but this will block the user interface and is not recommended at all.

Applications may query the current position and duration of the stream via gst_element_query_position() and gst_element_query_duration() and setting the format passed to GST_FORMAT_TIME. If the query was successful, the duration or position will have been returned in units of nanoseconds.


Advanced Usage: specifying the audio and video sink

By default, if no audio sink or video sink has been specified via the "audio-sink" or "video-sink" property, playbin will use the autoaudiosink and autovideosink elements to find the first-best available output method. This should work in most cases, but is not always desirable. Often either the user or application might want to specify more explicitly what to use for audio and video output.

If the application wants more control over how audio or video should be output, it may create the audio/video sink elements itself (for example using gst_element_factory_make()) and provide them to playbin using the "audio-sink" or "video-sink" property.

GNOME-based applications, for example, will usually want to create gconfaudiosink and gconfvideosink elements and make playbin use those, so that output happens to whatever the user has configured in the GNOME Multimedia System Selector configuration dialog.

The sink elements do not necessarily need to be ready-made sinks. It is possible to create container elements that look like a sink to playbin, but in reality contain a number of custom elements linked together. This can be achieved by creating a GstBin and putting elements in there and linking them, and then creating a sink GstGhostPad for the bin and pointing it to the sink pad of the first element within the bin. This can be used for a number of purposes, for example to force output to a particular format or to modify or observe the data before it is output.

It is also possible to 'suppress' audio and/or video output by using 'fakesink' elements (or capture it from there using the fakesink element's "handoff" signal, which, nota bene, is fired from the streaming thread!).


Retrieving Tags and Other Meta Data

Most of the common meta data (artist, title, etc.) can be retrieved by watching for TAG messages on the pipeline's bus (see above).

Other more specific meta information like width/height/framerate of video streams or samplerate/number of channels of audio streams can be obtained using the "stream-info" property, which will return a GList of stream info objects, one for each stream. These are opaque objects that can only be accessed via the standard GObject property interface, ie. g_object_get(). Each stream info object has the following properties:

  • "object" (GstObject) (the decoder source pad usually)
  • "type" (enum) (if this is an audio/video/subtitle stream)
  • "decoder" (string) (name of decoder used to decode this stream)
  • "mute" (boolean) (to mute or unmute this stream)
  • "caps" (GstCaps) (caps of the decoded stream)
  • "language-code" (string) (ISO-639 language code for this stream, mostly used for audio/subtitle streams)
  • "codec" (string) (format this stream was encoded in)

Stream information from the "stream-info" property is best queried once playbin has changed into PAUSED or PLAYING state (which can be detected via a state-changed message on the GstBus where old_state=READY and new_state=PAUSED), since before that the list might not be complete yet or not contain all available information (like language-codes).


Buffering

Playbin handles buffering automatically for the most part, but applications need to handle parts of the buffering process as well. Whenever playbin is buffering, it will post BUFFERING messages on the bus with a percentage value that shows the progress of the buffering process. Applications need to set playbin to PLAYING or PAUSED state in response to these messages. They may also want to convey the buffering progress to the user in some way. Here is how to extract the percentage information from the message (requires GStreamer >= 0.10.11):
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switch (GST_MESSAGE_TYPE (msg)) {
  case GST_MESSAGE_BUFFERING: {
    gint percent = 0;
    gst_message_parse_buffering (msg, &percent);
    g_print ("Buffering (%%u percent done)", percent);
    break;
  }
  ...
}
Note that applications should keep/set the pipeline in the PAUSED state when a BUFFERING message is received with a buffer percent value < 100 and set the pipeline back to PLAYING state when a BUFFERING message with a value of 100 percent is received (if PLAYING is the desired state, that is).


Embedding the video window in your application

By default, playbin (or rather the video sinks used) will create their own window. Applications will usually want to force output to a window of their own, however. This can be done using the GstXOverlay interface, which most video sinks implement. See the documentation there for more details.


Specifying which CD/DVD device to use

The device to use for CDs/DVDs needs to be set on the source element playbin creates before it is opened. The only way to do this at the moment is to connect to playbin's "notify::source" signal, which will be emitted by playbin when it has created the source element for a particular URI. In the signal callback you can check if the source element has a "device" property and set it appropriately. In future ways might be added to specify the device as part of the URI, but at the time of writing this is not possible yet.


Examples

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gst-launch -v playbin uri=file:///path/to/somefile.avi
This will play back the given AVI video file, given that the video and audio decoders required to decode the content are installed. Since no special audio sink or video sink is supplied (not possible via gst-launch), playbin will try to find a suitable audio and video sink automatically using the autoaudiosink and autovideosink elements.
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gst-launch -v playbin uri=cdda://4
This will play back track 4 on an audio CD in your disc drive (assuming the drive is detected automatically by the plugin).
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gst-launch -v playbin uri=dvd://1
This will play back title 1 of a DVD in your disc drive (assuming the drive is detected automatically by the plugin).

Synopsis

Element Information

plugin

playback

author

Wim Taymans <wim.taymans@gmail.com>

class

Generic/Bin/Player

Element Pads

Details

struct GstPlayBin

struct GstPlayBin;

High-level player element

Property Details

The "audio-sink" property

  "audio-sink"               GstElement*           : Read / Write

the audio output element to use (NULL = default sink).


The "frame" property

  "frame"                    GstBuffer*            : Read

The last frame (NULL = no video available).


The "subtitle-font-desc" property

  "subtitle-font-desc"       gchar*                : Write

Pango font description of font to be used for subtitle rendering.

Default value: NULL


The "video-sink" property

  "video-sink"               GstElement*           : Read / Write

the video output element to use (NULL = default sink).


The "vis-plugin" property

  "vis-plugin"               GstElement*           : Read / Write

the visualization element to use (NULL = none).


The "volume" property

  "volume"                   gdouble               : Read / Write

Get or set the current audio stream volume. 1.0 means 100%, 0.0 means mute. This uses a linear volume scale.

Allowed values: [0,10]

Default value: 1


The "connection-speed" property

  "connection-speed"         guint                 : Read / Write

Network connection speed in kbps (0 = unknown).

Default value: 0