# playbin

The purpose of this element is to decode and render the media contained in a given generic uri. The element extends `GstPipeline` and is typically used in playback situations.

Required features:

- accept and play any valid uri. This includes
- rendering video/audio
- overlaying subtitles on the video
- optionally read external subtitle files
- allow for hardware (non raw) sinks
- selection of audio/video/subtitle streams based on language.
- perform network buffering/incremental download
- gapless playback
- support for visualisations with configurable sizes
- ability to reject files that are too big, or of a format that would require too much CPU/memory usage.
- be very efficient with adding elements such as converters to reduce the amount of negotiation that has to happen.
- handle chained oggs. This includes having support for dynamic pad add and remove from a demuxer.

## Components

### decodebin

- performs the autoplugging of demuxers/decoders
- emits signals when for steering the autoplugging
- to decide if a non-raw media format is acceptable as output
- to sort the possible decoders for a non-raw format
- see also decodebin2 design doc

### uridecodebin

- combination of a source to handle the given uri, an optional queueing element and one or more decodebin2 elements to decode the non-raw streams.

### playsink

- handles display of audio/video/text.
- has request audio/video/text input pad. There is only one sinkpad per type. The requested pads define the configuration of the internal pipeline.
- allows for setting audio/video sinks or does automatic sink selection.
- allows for configuration of visualisation element.
- allows for enable/disable of visualisation, audio and video.

### playbin

- combination of one or more uridecodebin elements to read the uri and subtitle uri.
- support for queuing new media to support gapless playback.
- handles stream selection.
- uses playsink to display.
- selection of sinks and configuration of uridecodebin with raw output formats.

## Gapless playback feature

playbin has an `about-to-finish` signal. The application should configure a new uri (and optional suburi) in the callback. When the current media finishes, this new media will be played next.

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