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docs: add more docs around GstState and GstStateChange
Take reviewed docs from docs/design/part-state to have that more prominent inside the api docs. Add a few sentences to link things better together.
This commit is contained in:
Stefan Kost
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f65a81ae6d
commit
790e5d10c8
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@ -56,8 +56,8 @@
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*
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* Each element has a state (see #GstState). You can get and set the state
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* of an element with gst_element_get_state() and gst_element_set_state().
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* To get a string representation of a #GstState, use
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* gst_element_state_get_name().
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* Setting a state triggers a #GstStateChange. To get a string representation
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* of a #GstState, use gst_element_state_get_name().
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*
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* You can get and set a #GstClock on an element using gst_element_get_clock()
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* and gst_element_set_clock().
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@ -2063,8 +2063,8 @@ interrupted:
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*
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* This function returns %GST_STATE_CHANGE_NO_PREROLL if the element
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* successfully changed its state but is not able to provide data yet.
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* This mostly happens for live sources that only produce data in the PLAYING
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* state. While the state change return is equivalent to
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* This mostly happens for live sources that only produce data in
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* %GST_STATE_PLAYING. While the state change return is equivalent to
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* %GST_STATE_CHANGE_SUCCESS, it is returned to the application to signal that
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* some sink elements might not be able to complete their state change because
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* an element is not producing data to complete the preroll. When setting the
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150
gst/gstelement.h
150
gst/gstelement.h
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@ -31,13 +31,17 @@ typedef struct _GstElementClass GstElementClass;
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/* gstmessage.h needs State */
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/**
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* GstState:
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* @GST_STATE_VOID_PENDING : no pending state.
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* @GST_STATE_NULL : the NULL state or initial state of an element
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* @GST_STATE_READY : the element is ready to go to PAUSED
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* @GST_STATE_PAUSED : the element is PAUSED
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* @GST_STATE_PLAYING : the element is PLAYING
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* @GST_STATE_VOID_PENDING: no pending state.
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* @GST_STATE_NULL : the NULL state or initial state of an element.
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* @GST_STATE_READY : the element is ready to go to PAUSED.
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* @GST_STATE_PAUSED : the element is PAUSED, it is ready to accept and
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* process data. Sink elements however only accept one
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* buffer and then block.
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* @GST_STATE_PLAYING : the element is PLAYING, the #GstClock is running and
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* the data is flowing.
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*
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* The posible states an element can be in.
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* The posible states an element can be in. States can be chaged using
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* gst_element_set_state() and checked using gst_element_get_state().
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*/
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typedef enum {
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GST_STATE_VOID_PENDING = 0,
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@ -78,8 +82,8 @@ G_BEGIN_DECLS
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* @GST_STATE_CHANGE_SUCCESS : the state change succeeded
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* @GST_STATE_CHANGE_ASYNC : the state change will happen asynchronously
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* @GST_STATE_CHANGE_NO_PREROLL: the state change succeeded but the element
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* cannot produce data in PAUSED. This typically
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* happens with live sources.
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* cannot produce data in %GST_STATE_PAUSED.
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* This typically happens with live sources.
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*
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* The possible return values from a state change function. Only
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* @GST_STATE_CHANGE_FAILURE is a real failure.
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@ -173,15 +177,129 @@ typedef enum {
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/**
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* GstStateChange:
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* @GST_STATE_CHANGE_NULL_TO_READY : state change from NULL to READY
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* @GST_STATE_CHANGE_READY_TO_PAUSED : state change from READY to PAUSED
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* @GST_STATE_CHANGE_PAUSED_TO_PLAYING: state change from PAUSED to PLAYING
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* @GST_STATE_CHANGE_PLAYING_TO_PAUSED: state change from PLAYING to PAUSED
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* @GST_STATE_CHANGE_PAUSED_TO_READY : state change from PAUSED to READY
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* @GST_STATE_CHANGE_READY_TO_NULL : state change from READY to NULL
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* @GST_STATE_CHANGE_NULL_TO_READY : state change from NULL to READY.
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* <itemizedlist>
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* <listitem><para>
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* The element must check if the resources it needs are available. Device
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* sinks and -sources typically try to probe the device to constrain their
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* caps.
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* </para></listitem>
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* <listitem><para>
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* The element opens the device (in case feature need to be probed).
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* </para></listitem>
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* </itemizedlist>
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* @GST_STATE_CHANGE_READY_TO_PAUSED : state change from READY to PAUSED.
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* <itemizedlist>
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* <listitem><para>
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* The element pads are activated in order to receive data in PAUSED.
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* Streaming threads are started.
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* </para></listitem>
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* <listitem><para>
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* Some elements might need to return ASYNC and complete the state change
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* when they have enough information. It is a requirement for sinks to
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* return ASYNC and complete the state change when they receive the first
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* buffer or EOS event (preroll). Sinks also block the dataflow when in
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* PAUSED.
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* </para></listitem>
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* <listitem><para>
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* A pipeline resets the running_time to 0.
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* </para></listitem>
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* <listitem><para>
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* Live sources return NO_PREROLL and don't generate data.
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* </para></listitem>
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* </itemizedlist>
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* @GST_STATE_CHANGE_PAUSED_TO_PLAYING: state change from PAUSED to PLAYING.
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* <itemizedlist>
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* <listitem><para>
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* Most elements ignore this state change.
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* </para></listitem>
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* <listitem><para>
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* The pipeline selects a clock and distributes this to all the children
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* before setting them to PLAYING. This means that it is only alowed to
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* synchronize on the clock in the PLAYING state.
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* </para></listitem>
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* <listitem><para>
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* The pipeline uses the clock and the running_time to calculate the
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* base_time. The base_time is distributed to all children when performing
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* the state change.
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* </para></listitem>
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* <listitem><para>
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* Sink elements stop blocking on the preroll buffer or event and start
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* rendering the data.
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* </para></listitem>
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* <listitem><para>
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* Sinks can post the EOS message in the PLAYING state. It is not allowed to
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* post EOS when not in the PLAYING state.
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* </para></listitem>
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* <listitem><para>
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* While streaming in PAUSED or PLAYING elements can create and remove
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* sometimes pads.
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* </para></listitem>
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* <listitem><para>
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* Live sources start generating data and return SUCCESS.
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* </para></listitem>
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* </itemizedlist>
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* @GST_STATE_CHANGE_PLAYING_TO_PAUSED: state change from PLAYING to PAUSED.
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* <itemizedlist>
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* <listitem><para>
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* Most elements ignore this state change.
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* </para></listitem>
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* <listitem><para>
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* The pipeline calculates the running_time based on the last selected clock
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* and the base_time. It stores this information to continue playback when
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* going back to the PLAYING state.
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* </para></listitem>
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* <listitem><para>
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* Sinks unblock any clock wait calls.
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* </para></listitem>
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* <listitem><para>
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* When a sink does not have a pending buffer to play, it returns ASYNC from
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* this state change and completes the state change when it receives a new
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* buffer or an EOS event.
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* </para></listitem>
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* <listitem><para>
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* Any queued EOS messages are removed since they will be reposted when going
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* back to the PLAYING state. The EOS messages are queued in GstBins.
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* </para></listitem>
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* <listitem><para>
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* Live sources stop generating data and return NO_PREROLL.
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* </para></listitem>
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* </itemizedlist>
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* @GST_STATE_CHANGE_PAUSED_TO_READY : state change from PAUSED to READY.
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* <itemizedlist>
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* <listitem><para>
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* Sinks unblock any waits in the preroll.
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* </para></listitem>
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* <listitem><para>
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* Elements unblock any waits on devices
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* </para></listitem>
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* <listitem><para>
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* Chain or get_range functions return WRONG_STATE.
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* </para></listitem>
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* <listitem><para>
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* The element pads are deactivated so that streaming becomes impossible and
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* all streaming threads are stopped.
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* </para></listitem>
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* <listitem><para>
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* The sink forgets all negotiated formats
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* </para></listitem>
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* <listitem><para>
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* Elements remove all sometimes pads
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* </para></listitem>
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* </itemizedlist>
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* @GST_STATE_CHANGE_READY_TO_NULL : state change from READY to NULL.
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* <itemizedlist>
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* <listitem><para>
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* Elements close devices
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* </para></listitem>
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* <listitem><para>
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* Elements reset any internal state.
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* </para></listitem>
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* </itemizedlist>
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*
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* The different (interesting) state changes that are passed to the
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* state change functions of elements.
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* These are the different state changes an element goes through.
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* %GST_STATE_NULL ⇒ %GST_STATE_PLAYING is called an upwards state change
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* and %GST_STATE_PLAYING ⇒ %GST_STATE_NULL a downwards state change.
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*/
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typedef enum /*< flags=0 >*/
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{
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