StateChange

class StateChange

These are the different state changes an element goes through. NULL ⇒ PLAYING is called an upwards state change and PLAYING ⇒ NULL a downwards state change.

Methods

class StateChange
get_name(transition: StateChange) → str

Gets a string representing the given state transition.

Added in version 1.14.

Parameters:

transition – a StateChange to get the name of.

Fields

class StateChange
NULL_TO_NULL

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

NULL_TO_READY

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

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

State change from PAUSED to PLAYING. * Most elements ignore this state change. * The pipeline selects a Clock and distributes this to all the children

before setting them to PLAYING. This means that it is only allowed to synchronize on the Clock in the PLAYING state.

  • The pipeline uses the Clock 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 EOS in the PLAYING state. It is not allowed to post 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 SUCCESS.

PAUSED_TO_READY

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 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

State change from PLAYING to PAUSED. * Most elements ignore this state change. * The pipeline calculates the running_time based on the last selected

Clock and the base_time. It stores this information to continue playback when going back to the PLAYING state.

  • Sinks unblock any Clock 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 EOS.

  • Any queued EOS items are removed since they will be reposted when going back to the PLAYING state. The EOS messages are queued in Bin containers.

  • Live sources stop generating data and return NO_PREROLL.

PLAYING_TO_PLAYING

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

READY_TO_NULL

State change from READY to NULL. * Elements close devices * Elements reset any internal state.

READY_TO_PAUSED

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 ASYNC and complete the state change when they have enough information. It is a requirement for sinks to return ASYNC and complete the state change when they receive the first buffer or EOS (preroll). Sinks also block the dataflow when in PAUSED.

  • A pipeline resets the running_time to 0.

  • Live sources return NO_PREROLL and don’t generate data.

READY_TO_READY

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)