#[non_exhaustive]
pub enum StateChange {
    NullToReady,
    ReadyToPaused,
    PausedToPlaying,
    PlayingToPaused,
    PausedToReady,
    ReadyToNull,
    NullToNull,
    ReadyToReady,
    PausedToPaused,
    PlayingToPlaying,
    // some variants omitted
}
Expand description

These are the different state changes an element goes through. State::NullState::Playing is called an upwards state change and State::PlayingState::Null a downwards state change.

Variants (Non-exhaustive)

This enum is marked as non-exhaustive
Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

NullToReady

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).

ReadyToPaused

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 StateChangeReturn::Async and complete the state change when they have enough information. It is a requirement for sinks to return StateChangeReturn::Async and complete the state change when they receive the first buffer or EventType::Eos (preroll). Sinks also block the dataflow when in PAUSED.
  • A pipeline resets the running_time to 0.
  • Live sources return StateChangeReturn::NoPreroll and don’t generate data.

PausedToPlaying

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 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 StateChangeReturn::Success.

PlayingToPaused

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 StateChangeReturn::Async from this state change and completes the state change when it receives a new buffer or an EventType::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 Bin containers.
  • Live sources stop generating data and return StateChangeReturn::NoPreroll.

PausedToReady

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 FlowReturn::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

ReadyToNull

state change from READY to NULL.

  • Elements close devices
  • Elements reset any internal state.

NullToNull

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

ReadyToReady

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)

PausedToPaused

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)

PlayingToPlaying

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

Implementations

Trait Implementations

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Restrict a value to a certain interval. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

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This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

Returns the type identifier of Self.

Convert a value to a Value.

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Type to get the Type from. Read more

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Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Performs the conversion.

Performs the conversion.

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The resulting type after obtaining ownership.

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The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.