@type buffer() ::
  {:buffer, {Membrane.Pad.ref(), Membrane.Buffer.t() | [Membrane.Buffer.t()]}}

Sends buffers through a pad.

The pad must have output direction.

Allowed only when playback is playing.

@type common_actions() ::
  notify_parent()
  | start_timer()
  | timer_interval()
  | stop_timer()
  | terminate()
  | split()

Action that can be always returned from each of the callbacks.

@type demand() :: {:demand, {Membrane.Pad.ref(), demand_size()}}

Makes a demand on a pad.

The pad must have input direction and work in :manual flow control mode. This action does NOT entail sending demand through the pad, but just requesting some amount of data from pad's internal queue, which sends demands automatically when it runs out of data. If there is any data available at the pad, the data is passed to c:Membrane.WithInputPads.handle_buffer/4 callback. Invoked callback is guaranteed not to receive more data than demanded.

Demand size can be either a non-negative integer, that overrides existing demand, or a function that is passed current demand, and is to return the new demand.

Allowed only when playback is playing.

@type end_of_stream() :: {:end_of_stream, Membrane.Pad.ref()}

Marks that processing via a pad (output) has been finished and the pad instance won't be used anymore.

Triggers end_of_stream/3 callback at the receiver element. Allowed only when playback is in playing state.

@type event() :: {:event, {Membrane.Pad.ref(), Membrane.Event.t()}}

Sends an event through a pad (input or output).

Allowed only when playback is playing.

@type forward() ::
  {:forward,
   Membrane.Buffer.t()
   | [Membrane.Buffer.t()]
   | Membrane.StreamFormat.t()
   | Membrane.Event.t()
   | :end_of_stream}

Sends buffers/stream format/event/end of stream to all output pads of element (or to input pads when event occurs on the output pad).

Used by default implementations of Membrane.Element.WithInputPads.handle_stream_format/4, Membrane.Element.Base.handle_event/4 and Membrane.Element.WithInputPads.handle_end_of_stream/3 callbacks in filter.

Allowed only when all below conditions are met:

• element is filter,
• callback is Membrane.Element.WithInputPads.handle_buffer/4, Membrane.Element.WithInputPads.handle_stream_format/4, Membrane.Element.Base.handle_event/4 or Membrane.Element.WithInputPads.handle_end_of_stream/3
• playback is playing

Keep in mind that c:Membrane.WithInputPads.handle_buffer/4 can only forward buffers, Membrane.Element.WithInputPads.handle_stream_format/4 - stream formats. Membrane.Element.Base.handle_event/4 - events and Membrane.Element.WithInputPads.handle_end_of_stream/3 - ends of streams.

@type latency() :: {:latency, latency :: Membrane.Time.non_neg()}

This action sets the latency for the element.

This action is permitted only in callback Membrane.Element.Base.handle_init/2.

@type notify_parent() :: {:notify_parent, Membrane.ChildNotification.t()}

Sends a message to the parent.

@type pause_auto_demand() ::
  {:pause_auto_demand, Membrane.Pad.ref() | [Membrane.Pad.ref()]}

Pauses auto-demanding on the specific pad.

The pad must have input direction and work in :auto flow control mode.

This action does not guarantee that no more buffers will arrive on the specific pad, but ensures, that demand on this pad will not increase until returning Membrane.Element.Action.resume_auto_demand() action. Number of buffers, that will arrive on the pad, depends on the behaviour of the elements earlier in the pipeline.

When auto-demanding is already paused, this action has no effect.

@type redemand() :: {:redemand, Membrane.Pad.ref() | [Membrane.Pad.ref()]}

Executes Membrane.Element.WithOutputPads.handle_demand/5 callback for the given pad (or pads), that have demand greater than 0.

The pad must have output direction and work in pull mode.

Redemand in Sources and Endpoints

In case of Sources and Endpoints, :redemand is just a helper that simplifies element's code. The element doesn't need to generate the whole demand synchronously at handle_demand or store current demand size in its state, but it can just generate one buffer and return :redemand action. If there is still one or more buffers to produce, returning :redemand triggers the next invocation of handle_demand. In such case, the element is to produce next buffer and call :redemand again. If there are no more buffers demanded, handle_demand is not invoked and the loop ends. One more advantage of the approach with :redemand action is that produced buffers are sent one after another in separate messages and this can possibly improve the latency.

Redemand in Filters

Redemand in Filters is useful in a situation where not the entire demand of output pad has been satisfied and there is a need to send a demand for additional buffers through the input pad. A typical example of this situation is a parser that has not demanded enough bytes to parse the whole frame.

Usage limitations

Allowed only when playback is playing.

@type resume_auto_demand() ::
  {:resume_auto_demand, Membrane.Pad.ref() | [Membrane.Pad.ref()]}

Resumes auto-demanding on the specific pad.

The pad must have input direction and work in :auto flow control mode.

This action reverts the effects of Membrane.Element.Action.pause_auto_demand() action.

When auto demanding is not paused, this action has no effect.

@type setup() :: {:setup, :incomplete | :complete}

Action that manages the end of the component setup.

By default, component setup ends with the end of Membrane.Element.Base.handle_setup/2 callback. If {:setup, :incomplete} is returned there, setup lasts until {:setup, :complete} is returned from antoher callback.

Untils the setup lasts, the component won't enter :playing playback.

@type split() :: {:split, {callback_name :: atom(), args_list :: [[any()]]}}

Allows to split callback execution into multiple applications of another callback (called from now sub-callback).

Executions are synchronous in the element process, and each of them passes subsequent arguments from the args_list, along with the element state (passed as the last argument each time).

Return value of each execution of sub-callback can be any valid return value of the original callback (this also means sub-callback can return any action valid for the original callback, unless explicitly stated). Returned actions are executed immediately (they are NOT accumulated and executed after all sub-callback executions are finished).

Useful when a long action is to be undertaken, and partial results need to be returned before entire process finishes.

@type start_timer() ::
  {:start_timer,
   {timer_id :: any(),
    interval :: Ratio.t() | Membrane.Time.non_neg() | :no_interval}
   | {timer_id :: any(),
      interval :: Ratio.t() | Membrane.Time.non_neg() | :no_interval,
      clock :: Membrane.Clock.t()}}

Starts a timer that will invoke Membrane.Element.Base.handle_tick/3 callback every interval according to the given clock.

The timer's id is passed to the Membrane.Element.Base.handle_tick/3 callback and can be used for changing its interval via timer_interval/0 or stopping it via stop_timer/0.

If interval is set to :no_interval, the timer won't issue any ticks until the interval is set with timer_interval/0 action.

If no clock is passed, parent's clock is chosen.

Timers use Process.send_after/3 under the hood.

@type stop_timer() :: {:stop_timer, timer_id :: any()}

Stops a timer started with start_timer/0 action.

This action is atomic: stopping timer guarantees that no ticks will arrive from it.

@type stream_actions() ::
  event()
  | stream_format()
  | buffer()
  | demand()
  | pause_auto_demand()
  | resume_auto_demand()
  | end_of_stream()
  | redemand()

Actions that can be returned from callbacks when the element is in playback: :playing state.

@type stream_format() ::
  {:stream_format, {Membrane.Pad.ref(), Membrane.StreamFormat.t()}}

Sends stream format through a pad.

The pad must have output direction. Sent stream format must fit constraints on the pad.

Allowed only when playback is playing.

@type t() :: common_actions() | stream_actions() | latency() | forward() | setup()

Type that defines a union of actions that may be returned from most of the callbacks.

Depending on element type, callback, current playback and other circumstances there may be different actions available. Check the typespec and documentation of particular callbacks for details.

@type terminate() ::
  {:terminate, reason :: :normal | :shutdown | {:shutdown, term()} | term()}

Terminates element with given reason.

Termination reason follows the OTP semantics:

• Use :normal for graceful termination. Allowed only when the parent already requested termination, i.e. after Membrane.Element.Base.handle_terminate_request/2 is called
• If reason is neither :normal, :shutdown nor {:shutdown, term}, an error is logged

@type timer_interval() ::
  {:timer_interval,
   {timer_id :: any(),
    interval :: Ratio.t() | Membrane.Time.non_neg() | :no_interval}}

Changes interval of a timer started with start_timer/0.

Permitted only from Membrane.Element.Base.handle_tick/3, unless the interval was previously set to :no_interval.

If the interval is :no_interval, the timer won't issue any ticks until another timer_interval/0 action. Otherwise, the timer will issue ticks every new interval. The next tick after interval change is scheduled at new_interval + previous_time, where previous_time is the time of the latest tick or the time of returning start_timer/0 action if no tick has been sent yet. Note that if current_time - previous_time > new_interval, a burst of div(current_time - previous_time, new_interval) ticks is issued immediately.