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 from the negotiated caps on the sink pads of the sinks.

Buffering

1
2
3
4
5
6
7
8
9

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;
  }
  ...
}

Embedding the video window in your application

Specifying which CD/DVD device to use

Handling redirects

Some elements may post 'redirect' messages on the bus to tell the application to open another location. These are element messages containing a structure named 'redirect' along with a 'new-location' field of string type. The new location may be a relative or an absolute URI. Examples for such redirects can be found in many quicktime movie trailers.

Examples

1

gst-launch -v playbin uri=file:///path/to/somefile.avi

1

gst-launch -v playbin uri=cdda://4

1

gst-launch -v playbin uri=dvd://

struct GstPlayBin

struct GstPlayBin;

playbin element structure

enum GstPlayFlags

typedef enum {
  GST_PLAY_FLAG_VIDEO         = (1 << 0),
  GST_PLAY_FLAG_AUDIO         = (1 << 1),
  GST_PLAY_FLAG_TEXT          = (1 << 2),
  GST_PLAY_FLAG_VIS           = (1 << 3),
  GST_PLAY_FLAG_SOFT_VOLUME   = (1 << 4),
  GST_PLAY_FLAG_NATIVE_AUDIO  = (1 << 5),
  GST_PLAY_FLAG_NATIVE_VIDEO  = (1 << 6),
  GST_PLAY_FLAG_DOWNLOAD      = (1 << 7),
  GST_PLAY_FLAG_BUFFERING     = (1 << 8),
  GST_PLAY_FLAG_DEINTERLACE   = (1 << 9),
  GST_PLAY_FLAG_SOFT_COLORBALANCE = (1 << 10)
} GstPlayFlags;

Extra flags to configure the behaviour of the sinks.

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 = default).

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"         guint64               : Read / Write

Network connection speed in kbps (0 = unknown).

Allowed values: <= 18446744073709551

Default value: 0

The "av-offset" property

  "av-offset"                gint64                : Read / Write

Control the synchronisation offset between the audio and video streams. Positive values make the audio ahead of the video and negative values make the audio go behind the video.

Default value: 0

Since 0.10.30

The "buffer-duration" property

  "buffer-duration"          gint64                : Read / Write

Buffer duration when buffering network streams.

Allowed values: >= G_MAXULONG

Default value: -1

The "buffer-size" property

  "buffer-size"              gint                  : Read / Write

Buffer size when buffering network streams.

Allowed values: >= G_MAXULONG

Default value: -1

The "current-audio" property

  "current-audio"            gint                  : Read / Write

Get or set the currently playing audio stream. By default the first audio stream with data is played.

Allowed values: >= G_MAXULONG

Default value: -1

The "current-text" property

  "current-text"             gint                  : Read / Write

Get or set the currently playing subtitle stream. By default the first subtitle stream with data is played.

Allowed values: >= G_MAXULONG

Default value: -1

The "current-video" property

  "current-video"            gint                  : Read / Write

Get or set the currently playing video stream. By default the first video stream with data is played.

Allowed values: >= G_MAXULONG

Default value: -1

The "flags" property

  "flags"                    GstPlayFlags          : Read / Write

Control the behaviour of playbin.

Default value: Render the video stream|Render the audio stream|Render subtitles|Use software volume|Deinterlace video if necessary|Use software color balance

The "mute" property

  "mute"                     gboolean              : Read / Write

Mute the audio channel without changing the volume.

Default value: FALSE

The "n-audio" property

  "n-audio"                  gint                  : Read

Get the total number of available audio streams.

Allowed values: >= 0

Default value: 0

The "n-text" property

  "n-text"                   gint                  : Read

Get the total number of available subtitle streams.

Allowed values: >= 0

Default value: 0

The "n-video" property

  "n-video"                  gint                  : Read

Get the total number of available video streams.

Allowed values: >= 0

Default value: 0

The "ring-buffer-max-size" property

  "ring-buffer-max-size"     guint64               : Read / Write

The maximum size of the ring buffer in bytes. If set to 0, the ring buffer is disabled. Default 0.

Allowed values: <= G_MAXUINT

Default value: 0

Since 0.10.31

The "sample" property

  "sample"                   GstSample*            : Read

Get the currently rendered or prerolled sample in the video sink. The GstCaps in the sample will describe the format of the buffer.

The "source" property

  "source"                   GstElement*           : Read

Source element.

The "subtitle-encoding" property

  "subtitle-encoding"        gchar*                : Read / Write

Encoding to assume if input subtitles are not in UTF-8 encoding. If not set, the GST_SUBTITLE_ENCODING environment variable will be checked for an encoding to use. If that is not set either, ISO-8859-15 will be assumed.

Default value: NULL

The "suburi" property

  "suburi"                   gchar*                : Read / Write

Set the next subtitle URI that playbin will play. This property can be set from the about-to-finish signal to queue the next subtitle media file.

Default value: NULL

The "text-sink" property

  "text-sink"                GstElement*           : Read / Write

the text output element to use (NULL = default subtitleoverlay).

The "uri" property

  "uri"                      gchar*                : Read / Write

Set the next URI that playbin will play. This property can be set from the about-to-finish signal to queue the next media file.

Default value: NULL

The "current-suburi" property

  "current-suburi"           gchar*                : Read

The currently playing subtitle uri.

Default value: NULL

The "current-uri" property

  "current-uri"              gchar*                : Read

The currently playing uri.

Default value: NULL

The "force-aspect-ratio" property

  "force-aspect-ratio"       gboolean              : Read / Write

When enabled, scaling will respect original aspect ratio.

Default value: TRUE

The "audio-stream-combiner" property

  "audio-stream-combiner"    GstElement*           : Read / Write

Get or set the current audio stream combiner. By default, an input-selector is created and deleted as-needed.

The "text-stream-combiner" property

  "text-stream-combiner"     GstElement*           : Read / Write

Get or set the current text stream combiner. By default, an input-selector is created and deleted as-needed.

The "video-stream-combiner" property

  "video-stream-combiner"    GstElement*           : Read / Write

Get or set the current video stream combiner. By default, an input-selector is created and deleted as-needed.

The "about-to-finish" signal

void                user_function                      (GstPlayBin *playbin,
                                                        gpointer    user_data)      : Run Last

This signal is emitted when the current uri is about to finish. You can set the uri and suburi to make sure that playback continues.

This signal is emitted from the context of a GStreamer streaming thread.

The "audio-changed" signal

void                user_function                      (GstPlayBin *playbin,
                                                        gpointer    user_data)      : Run Last

This signal is emitted whenever the number or order of the audio streams has changed. The application will most likely want to select a new audio stream.

This signal may be emitted from the context of a GStreamer streaming thread. You can use gst_message_new_application() and gst_element_post_message() to notify your application's main thread.

The "audio-tags-changed" signal

void                user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Run Last

This signal is emitted whenever the tags of an audio stream have changed. The application will most likely want to get the new tags.

This signal may be emitted from the context of a GStreamer streaming thread. You can use gst_message_new_application() and gst_element_post_message() to notify your application's main thread.

Since 0.10.24

The "convert-sample" signal

GstSample*          user_function                      (GstPlayBin *playbin,
                                                        GstCaps    *caps,
                                                        gpointer    user_data)      : Action

Action signal to retrieve the currently playing video frame in the format specified by caps. If caps is NULL, no conversion will be performed and this function is equivalent to the "frame" property.

The "get-audio-pad" signal

GstPad*             user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Action

Action signal to retrieve the stream-combiner sinkpad for a specific audio stream. This pad can be used for notifications of caps changes, stream-specific queries, etc.

The "get-audio-tags" signal

GstTagList*         user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Action

Action signal to retrieve the tags of a specific audio stream number. This information can be used to select a stream.

The "get-text-pad" signal

GstPad*             user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Action

Action signal to retrieve the stream-combiner sinkpad for a specific text stream. This pad can be used for notifications of caps changes, stream-specific queries, etc.

The "get-text-tags" signal

GstTagList*         user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Action

Action signal to retrieve the tags of a specific text stream number. This information can be used to select a stream.

The "get-video-pad" signal

GstPad*             user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Action

Action signal to retrieve the stream-combiner sinkpad for a specific video stream. This pad can be used for notifications of caps changes, stream-specific queries, etc.

The "get-video-tags" signal

GstTagList*         user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Action

Action signal to retrieve the tags of a specific video stream number. This information can be used to select a stream.

The "source-setup" signal

void                user_function                      (GstPlayBin *playbin,
                                                        GstElement *source,
                                                        gpointer    user_data)      : Run Last

This signal is emitted after the source element has been created, so it can be configured by setting additional properties (e.g. set a proxy server for an http source, or set the device and read speed for an audio cd source). This is functionally equivalent to connecting to the notify::source signal, but more convenient.

This signal is usually emitted from the context of a GStreamer streaming thread.

Since 0.10.33

The "text-changed" signal

void                user_function                      (GstPlayBin *playbin,
                                                        gpointer    user_data)      : Run Last

This signal is emitted whenever the number or order of the text streams has changed. The application will most likely want to select a new text stream.

This signal may be emitted from the context of a GStreamer streaming thread. You can use gst_message_new_application() and gst_element_post_message() to notify your application's main thread.

The "text-tags-changed" signal

void                user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Run Last

This signal is emitted whenever the tags of a text stream have changed. The application will most likely want to get the new tags.

This signal may be emitted from the context of a GStreamer streaming thread. You can use gst_message_new_application() and gst_element_post_message() to notify your application's main thread.

Since 0.10.24

The "video-changed" signal

void                user_function                      (GstPlayBin *playbin,
                                                        gpointer    user_data)      : Run Last

This signal is emitted whenever the number or order of the video streams has changed. The application will most likely want to select a new video stream.

This signal is usually emitted from the context of a GStreamer streaming thread. You can use gst_message_new_application() and gst_element_post_message() to notify your application's main thread.

The "video-tags-changed" signal

void                user_function                      (GstPlayBin *playbin,
                                                        gint        stream,
                                                        gpointer    user_data)      : Run Last

This signal is emitted whenever the tags of a video stream have changed. The application will most likely want to get the new tags.

This signal may be emitted from the context of a GStreamer streaming thread. You can use gst_message_new_application() and gst_element_post_message() to notify your application's main thread.

Since 0.10.24