Enumeration StateChange

These are the different state changes an element goes through. %GST_STATE_NULL ⇒ %GST_STATE_PLAYING is called an upwards state change and %GST_STATE_PLAYING ⇒ %GST_STATE_NULL a downwards state change.

Index

Enumeration Members

NULL_TO_NULL

NULL_TO_NULL: number

state change from NULL to NULL. (Since: 1.14)

NULL_TO_READY

NULL_TO_READY: number

state change from NULL to READY.

The element must check if the resources it needs are available. Device sinks and -sources typically try to probe the device to constrain their caps.
The element opens the device (in case feature need to be probed).

PAUSED_TO_PAUSED

PAUSED_TO_PAUSED: number

state change from PAUSED to PAUSED. This might happen when elements were in PLAYING state and 'lost state', they should make sure to go back to real 'PAUSED' state (prerolling for example). (Since: 1.14)

PAUSED_TO_PLAYING

PAUSED_TO_PLAYING: number

state change from PAUSED to PLAYING.

Most elements ignore this state change.
The pipeline selects a #GstClock and distributes this to all the children before setting them to PLAYING. This means that it is only allowed to synchronize on the #GstClock in the PLAYING state.
The pipeline uses the #GstClock and the running_time to calculate the base_time. The base_time is distributed to all children when performing the state change.
Sink elements stop blocking on the preroll buffer or event and start rendering the data.
Sinks can post %GST_MESSAGE_EOS in the PLAYING state. It is not allowed to post %GST_MESSAGE_EOS when not in the PLAYING state.
While streaming in PAUSED or PLAYING elements can create and remove sometimes pads.
Live sources start generating data and return %GST_STATE_CHANGE_SUCCESS.

PAUSED_TO_READY

PAUSED_TO_READY: number

state change from PAUSED to READY.

Sinks unblock any waits in the preroll.
Elements unblock any waits on devices
Chain or get_range functions return %GST_FLOW_FLUSHING.
The element pads are deactivated so that streaming becomes impossible and all streaming threads are stopped.
The sink forgets all negotiated formats
Elements remove all sometimes pads

PLAYING_TO_PAUSED

PLAYING_TO_PAUSED: number

state change from PLAYING to PAUSED.

Most elements ignore this state change.
The pipeline calculates the running_time based on the last selected #GstClock and the base_time. It stores this information to continue playback when going back to the PLAYING state.
Sinks unblock any #GstClock wait calls.
When a sink does not have a pending buffer to play, it returns #GST_STATE_CHANGE_ASYNC from this state change and completes the state change when it receives a new buffer or an %GST_EVENT_EOS.
Any queued %GST_MESSAGE_EOS items are removed since they will be reposted when going back to the PLAYING state. The EOS messages are queued in #GstBin containers.
Live sources stop generating data and return %GST_STATE_CHANGE_NO_PREROLL.

PLAYING_TO_PLAYING

PLAYING_TO_PLAYING: number

state change from PLAYING to PLAYING. (Since: 1.14)

READY_TO_NULL

READY_TO_NULL: number

state change from READY to NULL.

Elements close devices
Elements reset any internal state.

READY_TO_PAUSED

READY_TO_PAUSED: number

state change from READY to PAUSED.

The element pads are activated in order to receive data in PAUSED. Streaming threads are started.
Some elements might need to return %GST_STATE_CHANGE_ASYNC and complete the state change when they have enough information. It is a requirement for sinks to return %GST_STATE_CHANGE_ASYNC and complete the state change when they receive the first buffer or %GST_EVENT_EOS (preroll). Sinks also block the dataflow when in PAUSED.
A pipeline resets the running_time to 0.
Live sources return %GST_STATE_CHANGE_NO_PREROLL and don't generate data.

READY_TO_READY

READY_TO_READY: number

state change from READY to READY, This might happen when going to PAUSED asynchronously failed, in that case elements should make sure they are in a proper, coherent READY state. (Since: 1.14)