playbin3

playbin3 provides a stand-alone everything-in-one abstraction for an audio and/or video player. It differs from the previous playbin (playbin2) by supporting publication and selection of available streams via the GstStreamCollection message and GST_EVENT_SELECT_STREAMS event API.

playbin3 is still experimental API and a technology preview. Its behaviour and exposed API is subject to change.

playbin3 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

  • auxiliary files - such as external subtitles and audio tracks

  • visualisations for audio files

  • subtitle support for video files. Subtitles can be store in external files.

  • stream selection between different video/audio/subtitles streams

  • meta info (tag) extraction

  • easy access to the last video sample

  • buffering when playing streams over a network

  • volume control with mute option

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 GstPlayBin3: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

Playbin3 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 occurred yet. Applications using playbin3 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 occurred (an ERROR message has been received on the bus) or the user wants to play a different track, playbin3 should be set back to READY or NULL state, then the GstPlayBin3:uri property should be set to the new location and then playbin3 be set to PLAYING state again.

Seeking can be done using gst_element_seek_simple or gst_element_seek on the playbin3 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.

Selecting streams

The recommended way to select streams (instead of the default selection) is to listen to GST_MESSAGE_STREAM_COLLECTION messages on the GstBus and send a GST_EVENT_SELECT_STREAMS on the pipeline with the selected streams. This provides more information and flexibility compared to the legacy GstPlayBin property and signal-based mechanism.

Note: The application should not assume that collections will not change throughout a single file. If it wishes to modify the default selection, it should always respond to new collections posted on the bus with a GST_EVENT_SELECT_STREAMS.

Advanced Usage: specifying the audio and video sink

By default, if no audio sink or video sink has been specified via the GstPlayBin3:audio-sink or GstPlayBin3:video-sink property, playbin3 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 playbin3 using the GstPlayBin3:audio-sink or GstPlayBin3:video-sink property.

GNOME-based applications, for example, will usually want to create gconfaudiosink and gconfvideosink elements and make playbin3 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 playbin3, 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

Playbin3 handles buffering automatically for the most part, but applications need to handle parts of the buffering process as well. Whenever playbin3 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 playbin3 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:

 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, playbin3 (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 GstVideoOverlay 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 playbin3 creates before it is opened. The most generic way of doing this is to connect to playbin3's "source-setup" signal, which will be emitted by playbin3 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 some cases the device can also be set as part of the URI, but it depends on the elements involved if this will work or not. For example, for DVD menu playback, the following syntax might work (if the resindvd plugin is used): dvd://[/path/to/device]

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

 gst-launch-1.0 -v playbin3 uri=file:///path/to/somefile.mp4

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 (via playbin3's audio-sink or video-sink properties) playbin3 will try to find a suitable audio and video sink automatically using the autoaudiosink and autovideosink elements.

 gst-launch-1.0 -v playbin3 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).

 gst-launch-1.0 -v playbin3 uri=dvd://

This will play back the DVD in your disc drive (assuming the drive is detected automatically by the plugin).

Hierarchy

GObject
    ╰──GInitiallyUnowned
        ╰──GstObject
            ╰──GstElement
                ╰──GstBin
                    ╰──GstPipeline
                        ╰──playbin3

Implemented interfaces

Factory details

Authors: – Wim Taymans

Classification:Generic/Bin/Player

Rank – none

Plugin – playback

Package – GStreamer Base Plug-ins

Signals

about-to-finish

about_to_finish_callback (GstElement * playbin,
                          gpointer udata)
def about_to_finish_callback (playbin, udata):
    #python callback for the 'about-to-finish' signal
function about_to_finish_callback(playbin: GstElement * playbin, udata: gpointer udata): {
    // javascript callback for the 'about-to-finish' signal
}

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.

Parameters:

playbin

a GstPlayBin3

udata
No description available

Flags: Run Last


convert-sample

GstSample *
convert_sample_callback (GstElement * playbin,
                         GstCaps * caps,
                         gpointer udata)
def convert_sample_callback (playbin, caps, udata):
    #python callback for the 'convert-sample' signal
function convert_sample_callback(playbin: GstElement * playbin, caps: GstCaps * caps, udata: gpointer udata): {
    // javascript callback for the 'convert-sample' signal
}

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 GstPlayBin3:sample property.

Parameters:

playbin

a GstPlayBin3

caps

the target format of the frame

udata
No description available
Returns ( GstSample * ) –

a GstSample of the current video frame converted to caps. The caps on the sample will describe the final layout of the buffer data. NULL is returned when no current buffer can be retrieved or when the conversion failed.

Flags: Run Last / Action


element-setup

element_setup_callback (GstElement * playbin,
                        GstElement * element,
                        gpointer udata)
def element_setup_callback (playbin, element, udata):
    #python callback for the 'element-setup' signal
function element_setup_callback(playbin: GstElement * playbin, element: GstElement * element, udata: gpointer udata): {
    // javascript callback for the 'element-setup' signal
}

This signal is emitted when a new element is added to playbin or any of its sub-bins. This signal can be used to configure elements, e.g. to set properties on decoders. This is functionally equivalent to connecting to the deep-element-added signal, but more convenient.

This signal is usually emitted from the context of a GStreamer streaming thread, so might be called at the same time as code running in the main application thread.

Parameters:

playbin

a GstPlayBin3

element

an element that was added to the playbin hierarchy

udata
No description available

Flags: Run Last

Since : 1.10


source-setup

source_setup_callback (GstElement * playbin,
                       GstElement * source,
                       gpointer udata)
def source_setup_callback (playbin, source, udata):
    #python callback for the 'source-setup' signal
function source_setup_callback(playbin: GstElement * playbin, source: GstElement * source, udata: gpointer udata): {
    // javascript callback for the 'source-setup' signal
}

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.

Parameters:

playbin

a GstPlayBin3

source

source element

udata
No description available

Flags: Run Last


Properties

audio-filter

“audio-filter” GstElement *

the audio filter(s) to apply, if possible

Flags : Read / Write


audio-sink

“audio-sink” GstElement *

Get or set the audio sink to use for audio output. If set to NULL, one will be auto-selected. To disable audio entirely, unset the AUDIO flag in the GstPlayBin3:flags property.

Flags : Read / Write


audio-stream-combiner

“audio-stream-combiner” GstElement *

Get or set the current audio stream combiner. By default, no element is used and the selected stream is used directly.

Flags : Read / Write


av-offset

“av-offset” gint64

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.

Flags : Read / Write

Default value : 0


buffer-duration

“buffer-duration” gint64

Buffer duration when buffering network streams

Flags : Read / Write

Default value : 18446744073709551615


buffer-size

“buffer-size” gint

Buffer size when buffering network streams

Flags : Read / Write

Default value : -1


connection-speed

“connection-speed” guint64

Network connection speed in kbps (0 = unknown)

Flags : Read / Write

Default value : 0


current-suburi

“current-suburi” gchararray

The currently playing subtitle uri.

Flags : Read

Default value : NULL


current-uri

“current-uri” gchararray

The currently playing uri.

Flags : Read

Default value : NULL


flags

“flags” GstPlayFlags *

Control the behaviour of playbin.

Flags : Read / Write

Default value : soft-colorbalance+deinterlace+buffering+soft-volume+text+audio+video


force-aspect-ratio

“force-aspect-ratio” gboolean

When enabled, scaling will respect original aspect ratio

Flags : Read / Write

Default value : true


mute

“mute” gboolean

Mute the audio channel without changing the volume

Flags : Read / Write

Default value : false


ring-buffer-max-size

“ring-buffer-max-size” guint64

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

Flags : Read / Write

Default value : 0


sample

“sample” GstSample *

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

Flags : Read


subtitle-encoding

“subtitle-encoding” gchararray

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.

Flags : Read / Write

Default value : NULL


subtitle-font-desc

“subtitle-font-desc” gchararray

Pango font description of font to be used for subtitle rendering

Flags : Read / Write

Default value : NULL


suburi

“suburi” gchararray

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.

Flags : Read / Write

Default value : NULL


text-offset

“text-offset” gint64

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

Flags : Read / Write

Default value : 0


text-sink

“text-sink” GstElement *

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

Flags : Read / Write


text-stream-combiner

“text-stream-combiner” GstElement *

Get or set the current text stream combiner. By default, no element is used and the selected stream is used directly.

Flags : Read / Write


uri

“uri” gchararray

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.

Flags : Read / Write

Default value : NULL


video-filter

“video-filter” GstElement *

the video filter(s) to apply, if possible

Flags : Read / Write


video-multiview-flags

“video-multiview-flags” GstVideoMultiviewFlags *

Override details of the multiview frame layout

Flags : Read / Write

Default value : none


video-multiview-mode

“video-multiview-mode” GstVideoMultiviewFramePacking *

Re-interpret a video stream as one of several frame-packed stereoscopic modes.

Flags : Read / Write

Default value : none (-1)


video-sink

“video-sink” GstElement *

Get or set the video sink to use for video output. If set to NULL, one will be auto-selected. To disable video entirely, unset the VIDEO flag in the GstPlayBin3:flags property.

Flags : Read / Write


video-stream-combiner

“video-stream-combiner” GstElement *

Get or set the current video stream combiner. By default, no element is used and the selected stream is used directly.

Flags : Read / Write


vis-plugin

“vis-plugin” GstElement *

the visualization element to use (NULL = default)

Flags : Read / Write


volume

“volume” gdouble

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

Flags : Read / Write

Default value : 1


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